counting number of inversions using merge sort

Question

i wrote the following code for counting the number of inversions in c++ using divide and conquer but it's not working can someone tell me what is going wrong here? Can someone explain what is wrong with my code and not post a link to any other related question as i have gone through them and cant figure out what is wrong with mine

#include <iostream>
#include <string>
using namespace std;
int merge_count_inverse(int left[],int right[])  /*counting number of inversion using merge sort*/
{
 int i=0;
 int c=0;
 int r=0;
 int j=0;
 int len_arr=0;
 int len_left=(sizeof(left)/sizeof(*left));
 int len_right=(sizeof(right)/sizeof(*right));
 len_arr=(len_left+len_right);
 int arr[len_arr];
 while((i<len_left)||(j<len_right))
  {
    if (left[i]<right[j])
     {
        arr[r]=left[i];
        r++;
        i++;
     }
    if (left[i]>right[j])
     {
        arr[r]=right[j];
        r++;
        j++;
        c=c+len_left-i;
     }
  }
return (c);

  }


int sort_count(int arr[])  
 {



int cou=0;
int l=0;
int r=0;
int m=0;


int len_arr=(sizeof(arr)/sizeof(*arr));

int middle=0;
middle=len_arr/2;

int left[middle];
int right[middle];



if (len_arr <2)
{
    return(0);
}
else
{
    for (int i=0;i<=(middle-1);i++)
    {
        left[i]=arr[i];
        right[i]=arr[middle+i];
    }
    l=l+sort_count(left);
    r=r+sort_count(right);
    m=m+merge_count_inverse(left,right);
    cou=cou+l+r+m;
    return(cou);
}

}

    int main()
     {
       int arr[8]={2,5,1,3,8,7,6,9};
       int len_arr=(sizeof(arr)/sizeof(*arr));


       int co=0;

       co+=sort_count(arr);
       cout<<co;

      }

this is too broad, you cannot assume someone will find time to study all your functions in a search for a (possible) error. You should tightened the domain and show us exact problem narrowed down to as few lines of code as possible — 4pie0, Jun 14 '14 at 11:36
i think the merge sort count is all right maybe the main or the sort-count or both. If i knew where i was going wrong i would have asked a more exact question although you are write too maybe i'll jsut wait for someone to show a bit of goodwill — arrhhh, Jun 14 '14 at 11:42

Vlad from Moscow · Accepted Answer · 2014-06-14T11:48:36.327

I did not look through all your code but it will be enough to point out that function sort_count is invalid. Its parameter is adjusted to int * So the calculation of len_arr has no sense

int sort_count(int arr[])  
 {

// ...
int len_arr=(sizeof(arr)/sizeof(*arr));

In fact the shown statement is equivalent to

int len_arr=(sizeof( int * )/sizeof( int ));

You should either define the function as a template function that has a parameter of type of a reference to an array or as a non-template function having two parameters. The second parameter will specify the size of the array.

The same is valid for function merge_count_inverse

int merge_count_inverse(int left[],int right[])  /*counting number of inversion using merge sort*/
{
 // ...
 int len_left=(sizeof(left)/sizeof(*left));
 int len_right=(sizeof(right)/sizeof(*right));

The calculations of len_left and len_right have no sense because left and right are not arrays. They are pointers int *

counting number of inversions using merge sort

1 Answers1