Sorting an array according to frequency and unique numbers. Where can my code be improved?












4












$begingroup$


So somebody asked me to create a code that orders unique numbers of an array according to their frequency, ie:



{1,3,3,4,4,4,4,4,2,2,5,5,5,5}


to



{4,5,3,2,1}


I'm a beginner and only started learning C last week so my code probably isn't optimal. I managed to get it in just over 100 lines without worrying too much about space. I haven't messed with memory allocation yet but I should start looking into it.



Any tips or feedback?



Edit: I will start commenting functions on the line before to make it more readable, thanks!



#include <stdio.h>
#include <string.h>


void CalculateFrequency(int numbers, int frequency) //Populates an array with the frequency of numbers in another
{
int hasSorted = 0;
do
{
hasSorted = 0;
for(int currentInt=0; currentInt<10; currentInt++)
{
for(int i=0; i<10; i++)
{
if(numbers[i] == currentInt)
{
frequency[currentInt]++;
hasSorted = 1;
}
}
}
if(hasSorted == 0)
{
break;
}
}while(hasSorted == 0);
}
void SortByFrequency(int numbers, int frequency) //Sorts an array according to the frequency of the numbers
{
int hasSorted = 0;
int temp = 0;
do
{
hasSorted = 0;
for(int i=0; i<10; i++)
{
for(int i=0; i<10; i++)
{
if(frequency[numbers[i]] < frequency[numbers[i+1]])
{
temp = numbers[i+1];
numbers[i+1] = numbers[i];
numbers[i] = temp;
hasSorted = 1;
}
}
}
if(hasSorted == 0)
{
break;
}
}while(hasSorted == 0);
}
int CountUniqueNumbers(int array, int arrayLength) //Counts unique numbers in an array
{
int count = 1; //At least 1 number
for(int i=0; i<arrayLength-1; i++)
{
if(array[i] != array[i+1])
{
count++;
}
}
return count;
}
int PopulateArrayByFrequencyAndReturnLength(int numbers, int sortedByFrequency)
{
int k = 0;
sortedByFrequency[0] = numbers[0];
for(int i=0; i<10; i++)
{
if(numbers[i] != numbers[i+1])
{
sortedByFrequency[k] = numbers[i];
k++;
}
}
return k;
}
int counter;

int main(void)
{
int numbers[10] = {1,2,2,2,5,7,8,8,8,8};
int frequency[10] = {0,0,0,0,0,0,0,0,0,0};
int sortedByFrequency[10] = {0,0,0,0,0,0,0,0,0,0};
int sortedByFrequencyTrueLength = 0;
int differentNumbers = 1; /*The array must have at least 1 number*/
int sizeofNumbersArray = 10;
int uniqueNumbersInArray = 0;
int i = 0;
/*print the numbers*/
printf("Numbers:t");
for(int i=0; i<10; i++)
{
printf("%d ", numbers[i]);
}
puts("");
/*Perform functions*/
CalculateFrequency(numbers, frequency);
SortByFrequency(numbers, frequency);
/*Get amount of unique numbers in the array*/
uniqueNumbersInArray = CountUniqueNumbers(numbers, sizeofNumbersArray);
/*Poupulate the unique number frequency array and get the true length*/
sortedByFrequencyTrueLength = PopulateArrayByFrequencyAndReturnLength(numbers, sortedByFrequency);
//Print unique number frequency array
printf("Numbers sorted by frequency:t");
for(i=0; i<sortedByFrequencyTrueLength; i++)
{
printf("%d ", sortedByFrequency[i]);
}
puts("");

return 0;
}









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  • 2




    $begingroup$
    Welcome to Code Review! I rolled back your last edit. After getting an answer you are not allowed to change your code anymore. This is to ensure that answers do not get invalidated and have to hit a moving target. If you have changed your code you can either post it as an answer (if it would constitute a code review) or ask a new question with your changed code (linking back to this one as reference). Refer to this post for more information
    $endgroup$
    – Sᴀᴍ Onᴇᴌᴀ
    4 hours ago












  • $begingroup$
    What should happen if there is a tie?
    $endgroup$
    – Deduplicator
    1 hour ago
















4












$begingroup$


So somebody asked me to create a code that orders unique numbers of an array according to their frequency, ie:



{1,3,3,4,4,4,4,4,2,2,5,5,5,5}


to



{4,5,3,2,1}


I'm a beginner and only started learning C last week so my code probably isn't optimal. I managed to get it in just over 100 lines without worrying too much about space. I haven't messed with memory allocation yet but I should start looking into it.



Any tips or feedback?



Edit: I will start commenting functions on the line before to make it more readable, thanks!



#include <stdio.h>
#include <string.h>


void CalculateFrequency(int numbers, int frequency) //Populates an array with the frequency of numbers in another
{
int hasSorted = 0;
do
{
hasSorted = 0;
for(int currentInt=0; currentInt<10; currentInt++)
{
for(int i=0; i<10; i++)
{
if(numbers[i] == currentInt)
{
frequency[currentInt]++;
hasSorted = 1;
}
}
}
if(hasSorted == 0)
{
break;
}
}while(hasSorted == 0);
}
void SortByFrequency(int numbers, int frequency) //Sorts an array according to the frequency of the numbers
{
int hasSorted = 0;
int temp = 0;
do
{
hasSorted = 0;
for(int i=0; i<10; i++)
{
for(int i=0; i<10; i++)
{
if(frequency[numbers[i]] < frequency[numbers[i+1]])
{
temp = numbers[i+1];
numbers[i+1] = numbers[i];
numbers[i] = temp;
hasSorted = 1;
}
}
}
if(hasSorted == 0)
{
break;
}
}while(hasSorted == 0);
}
int CountUniqueNumbers(int array, int arrayLength) //Counts unique numbers in an array
{
int count = 1; //At least 1 number
for(int i=0; i<arrayLength-1; i++)
{
if(array[i] != array[i+1])
{
count++;
}
}
return count;
}
int PopulateArrayByFrequencyAndReturnLength(int numbers, int sortedByFrequency)
{
int k = 0;
sortedByFrequency[0] = numbers[0];
for(int i=0; i<10; i++)
{
if(numbers[i] != numbers[i+1])
{
sortedByFrequency[k] = numbers[i];
k++;
}
}
return k;
}
int counter;

int main(void)
{
int numbers[10] = {1,2,2,2,5,7,8,8,8,8};
int frequency[10] = {0,0,0,0,0,0,0,0,0,0};
int sortedByFrequency[10] = {0,0,0,0,0,0,0,0,0,0};
int sortedByFrequencyTrueLength = 0;
int differentNumbers = 1; /*The array must have at least 1 number*/
int sizeofNumbersArray = 10;
int uniqueNumbersInArray = 0;
int i = 0;
/*print the numbers*/
printf("Numbers:t");
for(int i=0; i<10; i++)
{
printf("%d ", numbers[i]);
}
puts("");
/*Perform functions*/
CalculateFrequency(numbers, frequency);
SortByFrequency(numbers, frequency);
/*Get amount of unique numbers in the array*/
uniqueNumbersInArray = CountUniqueNumbers(numbers, sizeofNumbersArray);
/*Poupulate the unique number frequency array and get the true length*/
sortedByFrequencyTrueLength = PopulateArrayByFrequencyAndReturnLength(numbers, sortedByFrequency);
//Print unique number frequency array
printf("Numbers sorted by frequency:t");
for(i=0; i<sortedByFrequencyTrueLength; i++)
{
printf("%d ", sortedByFrequency[i]);
}
puts("");

return 0;
}









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  • 2




    $begingroup$
    Welcome to Code Review! I rolled back your last edit. After getting an answer you are not allowed to change your code anymore. This is to ensure that answers do not get invalidated and have to hit a moving target. If you have changed your code you can either post it as an answer (if it would constitute a code review) or ask a new question with your changed code (linking back to this one as reference). Refer to this post for more information
    $endgroup$
    – Sᴀᴍ Onᴇᴌᴀ
    4 hours ago












  • $begingroup$
    What should happen if there is a tie?
    $endgroup$
    – Deduplicator
    1 hour ago














4












4








4





$begingroup$


So somebody asked me to create a code that orders unique numbers of an array according to their frequency, ie:



{1,3,3,4,4,4,4,4,2,2,5,5,5,5}


to



{4,5,3,2,1}


I'm a beginner and only started learning C last week so my code probably isn't optimal. I managed to get it in just over 100 lines without worrying too much about space. I haven't messed with memory allocation yet but I should start looking into it.



Any tips or feedback?



Edit: I will start commenting functions on the line before to make it more readable, thanks!



#include <stdio.h>
#include <string.h>


void CalculateFrequency(int numbers, int frequency) //Populates an array with the frequency of numbers in another
{
int hasSorted = 0;
do
{
hasSorted = 0;
for(int currentInt=0; currentInt<10; currentInt++)
{
for(int i=0; i<10; i++)
{
if(numbers[i] == currentInt)
{
frequency[currentInt]++;
hasSorted = 1;
}
}
}
if(hasSorted == 0)
{
break;
}
}while(hasSorted == 0);
}
void SortByFrequency(int numbers, int frequency) //Sorts an array according to the frequency of the numbers
{
int hasSorted = 0;
int temp = 0;
do
{
hasSorted = 0;
for(int i=0; i<10; i++)
{
for(int i=0; i<10; i++)
{
if(frequency[numbers[i]] < frequency[numbers[i+1]])
{
temp = numbers[i+1];
numbers[i+1] = numbers[i];
numbers[i] = temp;
hasSorted = 1;
}
}
}
if(hasSorted == 0)
{
break;
}
}while(hasSorted == 0);
}
int CountUniqueNumbers(int array, int arrayLength) //Counts unique numbers in an array
{
int count = 1; //At least 1 number
for(int i=0; i<arrayLength-1; i++)
{
if(array[i] != array[i+1])
{
count++;
}
}
return count;
}
int PopulateArrayByFrequencyAndReturnLength(int numbers, int sortedByFrequency)
{
int k = 0;
sortedByFrequency[0] = numbers[0];
for(int i=0; i<10; i++)
{
if(numbers[i] != numbers[i+1])
{
sortedByFrequency[k] = numbers[i];
k++;
}
}
return k;
}
int counter;

int main(void)
{
int numbers[10] = {1,2,2,2,5,7,8,8,8,8};
int frequency[10] = {0,0,0,0,0,0,0,0,0,0};
int sortedByFrequency[10] = {0,0,0,0,0,0,0,0,0,0};
int sortedByFrequencyTrueLength = 0;
int differentNumbers = 1; /*The array must have at least 1 number*/
int sizeofNumbersArray = 10;
int uniqueNumbersInArray = 0;
int i = 0;
/*print the numbers*/
printf("Numbers:t");
for(int i=0; i<10; i++)
{
printf("%d ", numbers[i]);
}
puts("");
/*Perform functions*/
CalculateFrequency(numbers, frequency);
SortByFrequency(numbers, frequency);
/*Get amount of unique numbers in the array*/
uniqueNumbersInArray = CountUniqueNumbers(numbers, sizeofNumbersArray);
/*Poupulate the unique number frequency array and get the true length*/
sortedByFrequencyTrueLength = PopulateArrayByFrequencyAndReturnLength(numbers, sortedByFrequency);
//Print unique number frequency array
printf("Numbers sorted by frequency:t");
for(i=0; i<sortedByFrequencyTrueLength; i++)
{
printf("%d ", sortedByFrequency[i]);
}
puts("");

return 0;
}









share|improve this question









New contributor




Steffan Clent Davies is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







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So somebody asked me to create a code that orders unique numbers of an array according to their frequency, ie:



{1,3,3,4,4,4,4,4,2,2,5,5,5,5}


to



{4,5,3,2,1}


I'm a beginner and only started learning C last week so my code probably isn't optimal. I managed to get it in just over 100 lines without worrying too much about space. I haven't messed with memory allocation yet but I should start looking into it.



Any tips or feedback?



Edit: I will start commenting functions on the line before to make it more readable, thanks!



#include <stdio.h>
#include <string.h>


void CalculateFrequency(int numbers, int frequency) //Populates an array with the frequency of numbers in another
{
int hasSorted = 0;
do
{
hasSorted = 0;
for(int currentInt=0; currentInt<10; currentInt++)
{
for(int i=0; i<10; i++)
{
if(numbers[i] == currentInt)
{
frequency[currentInt]++;
hasSorted = 1;
}
}
}
if(hasSorted == 0)
{
break;
}
}while(hasSorted == 0);
}
void SortByFrequency(int numbers, int frequency) //Sorts an array according to the frequency of the numbers
{
int hasSorted = 0;
int temp = 0;
do
{
hasSorted = 0;
for(int i=0; i<10; i++)
{
for(int i=0; i<10; i++)
{
if(frequency[numbers[i]] < frequency[numbers[i+1]])
{
temp = numbers[i+1];
numbers[i+1] = numbers[i];
numbers[i] = temp;
hasSorted = 1;
}
}
}
if(hasSorted == 0)
{
break;
}
}while(hasSorted == 0);
}
int CountUniqueNumbers(int array, int arrayLength) //Counts unique numbers in an array
{
int count = 1; //At least 1 number
for(int i=0; i<arrayLength-1; i++)
{
if(array[i] != array[i+1])
{
count++;
}
}
return count;
}
int PopulateArrayByFrequencyAndReturnLength(int numbers, int sortedByFrequency)
{
int k = 0;
sortedByFrequency[0] = numbers[0];
for(int i=0; i<10; i++)
{
if(numbers[i] != numbers[i+1])
{
sortedByFrequency[k] = numbers[i];
k++;
}
}
return k;
}
int counter;

int main(void)
{
int numbers[10] = {1,2,2,2,5,7,8,8,8,8};
int frequency[10] = {0,0,0,0,0,0,0,0,0,0};
int sortedByFrequency[10] = {0,0,0,0,0,0,0,0,0,0};
int sortedByFrequencyTrueLength = 0;
int differentNumbers = 1; /*The array must have at least 1 number*/
int sizeofNumbersArray = 10;
int uniqueNumbersInArray = 0;
int i = 0;
/*print the numbers*/
printf("Numbers:t");
for(int i=0; i<10; i++)
{
printf("%d ", numbers[i]);
}
puts("");
/*Perform functions*/
CalculateFrequency(numbers, frequency);
SortByFrequency(numbers, frequency);
/*Get amount of unique numbers in the array*/
uniqueNumbersInArray = CountUniqueNumbers(numbers, sizeofNumbersArray);
/*Poupulate the unique number frequency array and get the true length*/
sortedByFrequencyTrueLength = PopulateArrayByFrequencyAndReturnLength(numbers, sortedByFrequency);
//Print unique number frequency array
printf("Numbers sorted by frequency:t");
for(i=0; i<sortedByFrequencyTrueLength; i++)
{
printf("%d ", sortedByFrequency[i]);
}
puts("");

return 0;
}






c array






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share|improve this question









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share|improve this question




share|improve this question








edited 4 hours ago









Sᴀᴍ Onᴇᴌᴀ

9,24662161




9,24662161






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asked 5 hours ago









Steffan Clent DaviesSteffan Clent Davies

1213




1213




New contributor




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New contributor





Steffan Clent Davies is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






Steffan Clent Davies is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.








  • 2




    $begingroup$
    Welcome to Code Review! I rolled back your last edit. After getting an answer you are not allowed to change your code anymore. This is to ensure that answers do not get invalidated and have to hit a moving target. If you have changed your code you can either post it as an answer (if it would constitute a code review) or ask a new question with your changed code (linking back to this one as reference). Refer to this post for more information
    $endgroup$
    – Sᴀᴍ Onᴇᴌᴀ
    4 hours ago












  • $begingroup$
    What should happen if there is a tie?
    $endgroup$
    – Deduplicator
    1 hour ago














  • 2




    $begingroup$
    Welcome to Code Review! I rolled back your last edit. After getting an answer you are not allowed to change your code anymore. This is to ensure that answers do not get invalidated and have to hit a moving target. If you have changed your code you can either post it as an answer (if it would constitute a code review) or ask a new question with your changed code (linking back to this one as reference). Refer to this post for more information
    $endgroup$
    – Sᴀᴍ Onᴇᴌᴀ
    4 hours ago












  • $begingroup$
    What should happen if there is a tie?
    $endgroup$
    – Deduplicator
    1 hour ago








2




2




$begingroup$
Welcome to Code Review! I rolled back your last edit. After getting an answer you are not allowed to change your code anymore. This is to ensure that answers do not get invalidated and have to hit a moving target. If you have changed your code you can either post it as an answer (if it would constitute a code review) or ask a new question with your changed code (linking back to this one as reference). Refer to this post for more information
$endgroup$
– Sᴀᴍ Onᴇᴌᴀ
4 hours ago






$begingroup$
Welcome to Code Review! I rolled back your last edit. After getting an answer you are not allowed to change your code anymore. This is to ensure that answers do not get invalidated and have to hit a moving target. If you have changed your code you can either post it as an answer (if it would constitute a code review) or ask a new question with your changed code (linking back to this one as reference). Refer to this post for more information
$endgroup$
– Sᴀᴍ Onᴇᴌᴀ
4 hours ago














$begingroup$
What should happen if there is a tie?
$endgroup$
– Deduplicator
1 hour ago




$begingroup$
What should happen if there is a tie?
$endgroup$
– Deduplicator
1 hour ago










2 Answers
2






active

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4












$begingroup$

I see a couple occurrences of:



do
{
hasSorted = 0;
...other things...
if(hasSorted == 0)
{
break;
}
}while(hasSorted == 0);


Did you mean if(hasSorted == 1) in those? If not, then you might want to just get rid of the whole if statement and replace the while condition with while(hasSorted != 0).





Also, comments that describe the whole function could look better on a separate line right before the function, so that the line doesn't get too long.






share|improve this answer









$endgroup$













  • $begingroup$
    Yes the break was redundant! Thanks for pointing that out!
    $endgroup$
    – Steffan Clent Davies
    4 hours ago



















1












$begingroup$

A few things I noticed:



Unused variables

The variables




  • differentNumbers

  • sizeofNumbersArray

  • uniqueNumbersInArray


are never used. That is particularly interesting because uniqueNumbersInArray is the return value of the function CountUniqueNumbers. Which means, that function is called for naught. As a matter of fact, the function PopulateArrayByFrequencyAndReturnLength returns the very same value!



Exceeding array bounds

On several occasions you access the arrays beyond their limits. As a first example, the function PopulateArrayByFrequencyAndReturnLength.



for(int i = 0; i < 10; i++)
{
if(numbers[i] != numbers[i+1])
{
sortedByFrequency[k] = numbers[i];
k++;
}
}


The index i runs all the way up to the last index, but the if accesses numbers[i+1], the element to the right. At the very last iteration you access numbers[10], the 11th element, but numbers is only 10 in length.



The same thing (for the same reasons) happens in SortByFrequency.



Logical errors

Running off the end of the array is the reason the function PopulateArrayByFrequencyAndReturnLength operates correctly. The counter k reacts to changes in the array. That means it wouldn't detect the last number in the array, since there is actually no change until the end. It does, however, detect a change, but accidentally because of the comparison with the element after the array.



You could account for the last number by manually incrementing k at the end. Or you can account manually for the first number in the array:



int PopulateArrayByFrequencyAndReturnLength(int numbers, int sortedByFrequency)
{
int k = 1;
sortedByFrequency[0] = numbers[0];
for(int i = 1; i < 10; i++)
{
if(numbers[i-1] != numbers[i])
{
sortedByFrequency[k++] = numbers[i];
}
}
return k;
}


Reducing Iterations



1. CalculateFrequency

The function CalculateFrequency runs in O(N^2) but can be done in linear time. If you notice, the number in the array is used as index into the frequency table - only in a complicated fashion. You can used those numbers directly and need to go through numbers only once:



void CalculateFrequency(int numbers, int frequency)
{
for(int i = 0; i < 10; i++)
frequency[numbers[i]]++;
}


2. SortByFrequency

That is a bubble sort algorithm. I noticed, that you use i for both the outer and the inner loop. The inner loop falls off the end of the array and in later iterations, the i numbers with lowest frequency are already sorted at the end. It is unnecessary to compare those again and again. That means, the inner loop can stop short by i:



void SortByFrequency(int numbers, int frequency)
{
int hasSorted = 0;
int temp = 0;
do
{
hasSorted = 0;
for(int i = 0; i < 9; i++)
{
for(int j = 0; j < 9-i; j++)
{
if(frequency[numbers[j]] < frequency[numbers[j+1]])
{
temp = numbers[j+1];
numbers[j+1] = numbers[j];
numbers[j] = temp;
hasSorted = 1;
}
}
}
} while (hasSorted);
}


Miscellaneous




  • As is, your algorithm doesn't scale well to large arrays with only few different numbers. And using the numbers as index into a frequency table will cause problems if the numbers themselves are very large. But optimisation here depends on the data that is to be expected.

  • The length of the array, hard coded inside your functions, should really be an additional parameter.

  • Array initialisation can be done shorter:


This sets all entries to zero:



int frequency[10] = {0};
int sortedByFrequency[10] = {0};


Or you could opt to use static arrays, they are initialised to zero:



static int frequency[10];
static int sortedByFrequency[10];





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    2 Answers
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    4












    $begingroup$

    I see a couple occurrences of:



    do
    {
    hasSorted = 0;
    ...other things...
    if(hasSorted == 0)
    {
    break;
    }
    }while(hasSorted == 0);


    Did you mean if(hasSorted == 1) in those? If not, then you might want to just get rid of the whole if statement and replace the while condition with while(hasSorted != 0).





    Also, comments that describe the whole function could look better on a separate line right before the function, so that the line doesn't get too long.






    share|improve this answer









    $endgroup$













    • $begingroup$
      Yes the break was redundant! Thanks for pointing that out!
      $endgroup$
      – Steffan Clent Davies
      4 hours ago
















    4












    $begingroup$

    I see a couple occurrences of:



    do
    {
    hasSorted = 0;
    ...other things...
    if(hasSorted == 0)
    {
    break;
    }
    }while(hasSorted == 0);


    Did you mean if(hasSorted == 1) in those? If not, then you might want to just get rid of the whole if statement and replace the while condition with while(hasSorted != 0).





    Also, comments that describe the whole function could look better on a separate line right before the function, so that the line doesn't get too long.






    share|improve this answer









    $endgroup$













    • $begingroup$
      Yes the break was redundant! Thanks for pointing that out!
      $endgroup$
      – Steffan Clent Davies
      4 hours ago














    4












    4








    4





    $begingroup$

    I see a couple occurrences of:



    do
    {
    hasSorted = 0;
    ...other things...
    if(hasSorted == 0)
    {
    break;
    }
    }while(hasSorted == 0);


    Did you mean if(hasSorted == 1) in those? If not, then you might want to just get rid of the whole if statement and replace the while condition with while(hasSorted != 0).





    Also, comments that describe the whole function could look better on a separate line right before the function, so that the line doesn't get too long.






    share|improve this answer









    $endgroup$



    I see a couple occurrences of:



    do
    {
    hasSorted = 0;
    ...other things...
    if(hasSorted == 0)
    {
    break;
    }
    }while(hasSorted == 0);


    Did you mean if(hasSorted == 1) in those? If not, then you might want to just get rid of the whole if statement and replace the while condition with while(hasSorted != 0).





    Also, comments that describe the whole function could look better on a separate line right before the function, so that the line doesn't get too long.







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered 5 hours ago









    snetchsnetch

    22617




    22617












    • $begingroup$
      Yes the break was redundant! Thanks for pointing that out!
      $endgroup$
      – Steffan Clent Davies
      4 hours ago


















    • $begingroup$
      Yes the break was redundant! Thanks for pointing that out!
      $endgroup$
      – Steffan Clent Davies
      4 hours ago
















    $begingroup$
    Yes the break was redundant! Thanks for pointing that out!
    $endgroup$
    – Steffan Clent Davies
    4 hours ago




    $begingroup$
    Yes the break was redundant! Thanks for pointing that out!
    $endgroup$
    – Steffan Clent Davies
    4 hours ago













    1












    $begingroup$

    A few things I noticed:



    Unused variables

    The variables




    • differentNumbers

    • sizeofNumbersArray

    • uniqueNumbersInArray


    are never used. That is particularly interesting because uniqueNumbersInArray is the return value of the function CountUniqueNumbers. Which means, that function is called for naught. As a matter of fact, the function PopulateArrayByFrequencyAndReturnLength returns the very same value!



    Exceeding array bounds

    On several occasions you access the arrays beyond their limits. As a first example, the function PopulateArrayByFrequencyAndReturnLength.



    for(int i = 0; i < 10; i++)
    {
    if(numbers[i] != numbers[i+1])
    {
    sortedByFrequency[k] = numbers[i];
    k++;
    }
    }


    The index i runs all the way up to the last index, but the if accesses numbers[i+1], the element to the right. At the very last iteration you access numbers[10], the 11th element, but numbers is only 10 in length.



    The same thing (for the same reasons) happens in SortByFrequency.



    Logical errors

    Running off the end of the array is the reason the function PopulateArrayByFrequencyAndReturnLength operates correctly. The counter k reacts to changes in the array. That means it wouldn't detect the last number in the array, since there is actually no change until the end. It does, however, detect a change, but accidentally because of the comparison with the element after the array.



    You could account for the last number by manually incrementing k at the end. Or you can account manually for the first number in the array:



    int PopulateArrayByFrequencyAndReturnLength(int numbers, int sortedByFrequency)
    {
    int k = 1;
    sortedByFrequency[0] = numbers[0];
    for(int i = 1; i < 10; i++)
    {
    if(numbers[i-1] != numbers[i])
    {
    sortedByFrequency[k++] = numbers[i];
    }
    }
    return k;
    }


    Reducing Iterations



    1. CalculateFrequency

    The function CalculateFrequency runs in O(N^2) but can be done in linear time. If you notice, the number in the array is used as index into the frequency table - only in a complicated fashion. You can used those numbers directly and need to go through numbers only once:



    void CalculateFrequency(int numbers, int frequency)
    {
    for(int i = 0; i < 10; i++)
    frequency[numbers[i]]++;
    }


    2. SortByFrequency

    That is a bubble sort algorithm. I noticed, that you use i for both the outer and the inner loop. The inner loop falls off the end of the array and in later iterations, the i numbers with lowest frequency are already sorted at the end. It is unnecessary to compare those again and again. That means, the inner loop can stop short by i:



    void SortByFrequency(int numbers, int frequency)
    {
    int hasSorted = 0;
    int temp = 0;
    do
    {
    hasSorted = 0;
    for(int i = 0; i < 9; i++)
    {
    for(int j = 0; j < 9-i; j++)
    {
    if(frequency[numbers[j]] < frequency[numbers[j+1]])
    {
    temp = numbers[j+1];
    numbers[j+1] = numbers[j];
    numbers[j] = temp;
    hasSorted = 1;
    }
    }
    }
    } while (hasSorted);
    }


    Miscellaneous




    • As is, your algorithm doesn't scale well to large arrays with only few different numbers. And using the numbers as index into a frequency table will cause problems if the numbers themselves are very large. But optimisation here depends on the data that is to be expected.

    • The length of the array, hard coded inside your functions, should really be an additional parameter.

    • Array initialisation can be done shorter:


    This sets all entries to zero:



    int frequency[10] = {0};
    int sortedByFrequency[10] = {0};


    Or you could opt to use static arrays, they are initialised to zero:



    static int frequency[10];
    static int sortedByFrequency[10];





    share|improve this answer









    $endgroup$


















      1












      $begingroup$

      A few things I noticed:



      Unused variables

      The variables




      • differentNumbers

      • sizeofNumbersArray

      • uniqueNumbersInArray


      are never used. That is particularly interesting because uniqueNumbersInArray is the return value of the function CountUniqueNumbers. Which means, that function is called for naught. As a matter of fact, the function PopulateArrayByFrequencyAndReturnLength returns the very same value!



      Exceeding array bounds

      On several occasions you access the arrays beyond their limits. As a first example, the function PopulateArrayByFrequencyAndReturnLength.



      for(int i = 0; i < 10; i++)
      {
      if(numbers[i] != numbers[i+1])
      {
      sortedByFrequency[k] = numbers[i];
      k++;
      }
      }


      The index i runs all the way up to the last index, but the if accesses numbers[i+1], the element to the right. At the very last iteration you access numbers[10], the 11th element, but numbers is only 10 in length.



      The same thing (for the same reasons) happens in SortByFrequency.



      Logical errors

      Running off the end of the array is the reason the function PopulateArrayByFrequencyAndReturnLength operates correctly. The counter k reacts to changes in the array. That means it wouldn't detect the last number in the array, since there is actually no change until the end. It does, however, detect a change, but accidentally because of the comparison with the element after the array.



      You could account for the last number by manually incrementing k at the end. Or you can account manually for the first number in the array:



      int PopulateArrayByFrequencyAndReturnLength(int numbers, int sortedByFrequency)
      {
      int k = 1;
      sortedByFrequency[0] = numbers[0];
      for(int i = 1; i < 10; i++)
      {
      if(numbers[i-1] != numbers[i])
      {
      sortedByFrequency[k++] = numbers[i];
      }
      }
      return k;
      }


      Reducing Iterations



      1. CalculateFrequency

      The function CalculateFrequency runs in O(N^2) but can be done in linear time. If you notice, the number in the array is used as index into the frequency table - only in a complicated fashion. You can used those numbers directly and need to go through numbers only once:



      void CalculateFrequency(int numbers, int frequency)
      {
      for(int i = 0; i < 10; i++)
      frequency[numbers[i]]++;
      }


      2. SortByFrequency

      That is a bubble sort algorithm. I noticed, that you use i for both the outer and the inner loop. The inner loop falls off the end of the array and in later iterations, the i numbers with lowest frequency are already sorted at the end. It is unnecessary to compare those again and again. That means, the inner loop can stop short by i:



      void SortByFrequency(int numbers, int frequency)
      {
      int hasSorted = 0;
      int temp = 0;
      do
      {
      hasSorted = 0;
      for(int i = 0; i < 9; i++)
      {
      for(int j = 0; j < 9-i; j++)
      {
      if(frequency[numbers[j]] < frequency[numbers[j+1]])
      {
      temp = numbers[j+1];
      numbers[j+1] = numbers[j];
      numbers[j] = temp;
      hasSorted = 1;
      }
      }
      }
      } while (hasSorted);
      }


      Miscellaneous




      • As is, your algorithm doesn't scale well to large arrays with only few different numbers. And using the numbers as index into a frequency table will cause problems if the numbers themselves are very large. But optimisation here depends on the data that is to be expected.

      • The length of the array, hard coded inside your functions, should really be an additional parameter.

      • Array initialisation can be done shorter:


      This sets all entries to zero:



      int frequency[10] = {0};
      int sortedByFrequency[10] = {0};


      Or you could opt to use static arrays, they are initialised to zero:



      static int frequency[10];
      static int sortedByFrequency[10];





      share|improve this answer









      $endgroup$
















        1












        1








        1





        $begingroup$

        A few things I noticed:



        Unused variables

        The variables




        • differentNumbers

        • sizeofNumbersArray

        • uniqueNumbersInArray


        are never used. That is particularly interesting because uniqueNumbersInArray is the return value of the function CountUniqueNumbers. Which means, that function is called for naught. As a matter of fact, the function PopulateArrayByFrequencyAndReturnLength returns the very same value!



        Exceeding array bounds

        On several occasions you access the arrays beyond their limits. As a first example, the function PopulateArrayByFrequencyAndReturnLength.



        for(int i = 0; i < 10; i++)
        {
        if(numbers[i] != numbers[i+1])
        {
        sortedByFrequency[k] = numbers[i];
        k++;
        }
        }


        The index i runs all the way up to the last index, but the if accesses numbers[i+1], the element to the right. At the very last iteration you access numbers[10], the 11th element, but numbers is only 10 in length.



        The same thing (for the same reasons) happens in SortByFrequency.



        Logical errors

        Running off the end of the array is the reason the function PopulateArrayByFrequencyAndReturnLength operates correctly. The counter k reacts to changes in the array. That means it wouldn't detect the last number in the array, since there is actually no change until the end. It does, however, detect a change, but accidentally because of the comparison with the element after the array.



        You could account for the last number by manually incrementing k at the end. Or you can account manually for the first number in the array:



        int PopulateArrayByFrequencyAndReturnLength(int numbers, int sortedByFrequency)
        {
        int k = 1;
        sortedByFrequency[0] = numbers[0];
        for(int i = 1; i < 10; i++)
        {
        if(numbers[i-1] != numbers[i])
        {
        sortedByFrequency[k++] = numbers[i];
        }
        }
        return k;
        }


        Reducing Iterations



        1. CalculateFrequency

        The function CalculateFrequency runs in O(N^2) but can be done in linear time. If you notice, the number in the array is used as index into the frequency table - only in a complicated fashion. You can used those numbers directly and need to go through numbers only once:



        void CalculateFrequency(int numbers, int frequency)
        {
        for(int i = 0; i < 10; i++)
        frequency[numbers[i]]++;
        }


        2. SortByFrequency

        That is a bubble sort algorithm. I noticed, that you use i for both the outer and the inner loop. The inner loop falls off the end of the array and in later iterations, the i numbers with lowest frequency are already sorted at the end. It is unnecessary to compare those again and again. That means, the inner loop can stop short by i:



        void SortByFrequency(int numbers, int frequency)
        {
        int hasSorted = 0;
        int temp = 0;
        do
        {
        hasSorted = 0;
        for(int i = 0; i < 9; i++)
        {
        for(int j = 0; j < 9-i; j++)
        {
        if(frequency[numbers[j]] < frequency[numbers[j+1]])
        {
        temp = numbers[j+1];
        numbers[j+1] = numbers[j];
        numbers[j] = temp;
        hasSorted = 1;
        }
        }
        }
        } while (hasSorted);
        }


        Miscellaneous




        • As is, your algorithm doesn't scale well to large arrays with only few different numbers. And using the numbers as index into a frequency table will cause problems if the numbers themselves are very large. But optimisation here depends on the data that is to be expected.

        • The length of the array, hard coded inside your functions, should really be an additional parameter.

        • Array initialisation can be done shorter:


        This sets all entries to zero:



        int frequency[10] = {0};
        int sortedByFrequency[10] = {0};


        Or you could opt to use static arrays, they are initialised to zero:



        static int frequency[10];
        static int sortedByFrequency[10];





        share|improve this answer









        $endgroup$



        A few things I noticed:



        Unused variables

        The variables




        • differentNumbers

        • sizeofNumbersArray

        • uniqueNumbersInArray


        are never used. That is particularly interesting because uniqueNumbersInArray is the return value of the function CountUniqueNumbers. Which means, that function is called for naught. As a matter of fact, the function PopulateArrayByFrequencyAndReturnLength returns the very same value!



        Exceeding array bounds

        On several occasions you access the arrays beyond their limits. As a first example, the function PopulateArrayByFrequencyAndReturnLength.



        for(int i = 0; i < 10; i++)
        {
        if(numbers[i] != numbers[i+1])
        {
        sortedByFrequency[k] = numbers[i];
        k++;
        }
        }


        The index i runs all the way up to the last index, but the if accesses numbers[i+1], the element to the right. At the very last iteration you access numbers[10], the 11th element, but numbers is only 10 in length.



        The same thing (for the same reasons) happens in SortByFrequency.



        Logical errors

        Running off the end of the array is the reason the function PopulateArrayByFrequencyAndReturnLength operates correctly. The counter k reacts to changes in the array. That means it wouldn't detect the last number in the array, since there is actually no change until the end. It does, however, detect a change, but accidentally because of the comparison with the element after the array.



        You could account for the last number by manually incrementing k at the end. Or you can account manually for the first number in the array:



        int PopulateArrayByFrequencyAndReturnLength(int numbers, int sortedByFrequency)
        {
        int k = 1;
        sortedByFrequency[0] = numbers[0];
        for(int i = 1; i < 10; i++)
        {
        if(numbers[i-1] != numbers[i])
        {
        sortedByFrequency[k++] = numbers[i];
        }
        }
        return k;
        }


        Reducing Iterations



        1. CalculateFrequency

        The function CalculateFrequency runs in O(N^2) but can be done in linear time. If you notice, the number in the array is used as index into the frequency table - only in a complicated fashion. You can used those numbers directly and need to go through numbers only once:



        void CalculateFrequency(int numbers, int frequency)
        {
        for(int i = 0; i < 10; i++)
        frequency[numbers[i]]++;
        }


        2. SortByFrequency

        That is a bubble sort algorithm. I noticed, that you use i for both the outer and the inner loop. The inner loop falls off the end of the array and in later iterations, the i numbers with lowest frequency are already sorted at the end. It is unnecessary to compare those again and again. That means, the inner loop can stop short by i:



        void SortByFrequency(int numbers, int frequency)
        {
        int hasSorted = 0;
        int temp = 0;
        do
        {
        hasSorted = 0;
        for(int i = 0; i < 9; i++)
        {
        for(int j = 0; j < 9-i; j++)
        {
        if(frequency[numbers[j]] < frequency[numbers[j+1]])
        {
        temp = numbers[j+1];
        numbers[j+1] = numbers[j];
        numbers[j] = temp;
        hasSorted = 1;
        }
        }
        }
        } while (hasSorted);
        }


        Miscellaneous




        • As is, your algorithm doesn't scale well to large arrays with only few different numbers. And using the numbers as index into a frequency table will cause problems if the numbers themselves are very large. But optimisation here depends on the data that is to be expected.

        • The length of the array, hard coded inside your functions, should really be an additional parameter.

        • Array initialisation can be done shorter:


        This sets all entries to zero:



        int frequency[10] = {0};
        int sortedByFrequency[10] = {0};


        Or you could opt to use static arrays, they are initialised to zero:



        static int frequency[10];
        static int sortedByFrequency[10];






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 1 hour ago









        jgbjgb

        353




        353






















            Steffan Clent Davies is a new contributor. Be nice, and check out our Code of Conduct.










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            Steffan Clent Davies is a new contributor. Be nice, and check out our Code of Conduct.













            Steffan Clent Davies is a new contributor. Be nice, and check out our Code of Conduct.












            Steffan Clent Davies is a new contributor. Be nice, and check out our Code of Conduct.
















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