Number of swaps to sort when only adjacent swapping allowed | C ++ program to count number of swaps required to sort an array when only swapping of adjacent elements is allowed . ; This function merges two sorted arrays and returns inversion count in the arrays . ; i is index for left subarray ; j is index for right subarray ; k is index for resultant merged subarray ; this is tricky -- see above explanation / diagram for merge ( ) ; Copy the remaining elements of left subarray ( if there are any ) to temp ; Copy the remaining elements of right subarray ( if there are any ) to temp ; Copy back the merged elements to original array ; An auxiliary recursive function that sorts the input array and returns the number of inversions in the array . ; Divide the array into two parts and call _mergeSortAndCountInv ( ) for each of the parts ; Inversion count will be sum of inversions in left - part , right - part and number of inversions in merging ; Merge the two parts ; This function sorts the input array and returns the number of inversions in the array ; Driver progra to test above functions
#include <bits/stdc++.h> NEW_LINE int merge ( int arr [ ] , int temp [ ] , int left , int mid , int right ) { int inv_count = 0 ; int i = left ; int j = mid ; int k = left ; while ( ( i <= mid - 1 ) && ( j <= right ) ) { if ( arr [ i ] <= arr [ j ] ) temp [ k ++ ] = arr [ i ++ ] ; else { temp [ k ++ ] = arr [ j ++ ] ; inv_count = inv_count + ( mid - i ) ; } } while ( i <= mid - 1 ) temp [ k ++ ] = arr [ i ++ ] ; while ( j <= right ) temp [ k ++ ] = arr [ j ++ ] ; for ( i = left ; i <= right ; i ++ ) arr [ i ] = temp [ i ] ; return inv_count ; } int _mergeSort ( int arr [ ] , int temp [ ] , int left , int right ) { int mid , inv_count = 0 ; if ( right > left ) { mid = ( right + left ) / 2 ; inv_count = _mergeSort ( arr , temp , left , mid ) ; inv_count += _mergeSort ( arr , temp , mid + 1 , right ) ; inv_count += merge ( arr , temp , left , mid + 1 , right ) ; } return inv_count ; } int countSwaps ( int arr [ ] , int n ) { int temp [ n ] ; return _mergeSort ( arr , temp , 0 , n - 1 ) ; } int main ( int argv , char * * args ) { int arr [ ] = { 1 , 20 , 6 , 4 , 5 } ; int n = sizeof ( arr ) / sizeof ( arr [ 0 ] ) ; printf ( " Number ▁ of ▁ swaps ▁ is ▁ % d ▁ STRNEWLINE " , countSwaps ( arr , n ) ) ; return 0 ; }