Number of swaps to sort when only adjacent swapping 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
def merge ( arr , temp , left , mid , right ) : NEW_LINE INDENT inv_count = 0 NEW_LINE DEDENT i = left NEW_LINE j = mid NEW_LINE k = left NEW_LINE INDENT while ( ( i <= mid - 1 ) and ( j <= right ) ) : NEW_LINE INDENT if ( arr [ i ] <= arr [ j ] ) : NEW_LINE INDENT temp [ k ] = arr [ i ] NEW_LINE k += 1 NEW_LINE i += 1 NEW_LINE DEDENT else : NEW_LINE INDENT temp [ k ] = arr [ j ] NEW_LINE k += 1 NEW_LINE j += 1 NEW_LINE inv_count = inv_count + ( mid - i ) NEW_LINE DEDENT DEDENT while ( i <= mid - 1 ) : NEW_LINE INDENT temp [ k ] = arr [ i ] NEW_LINE k += 1 NEW_LINE i += 1 NEW_LINE DEDENT while ( j <= right ) : NEW_LINE INDENT temp [ k ] = arr [ j ] NEW_LINE k += 1 NEW_LINE j += 1 NEW_LINE DEDENT for i in range ( left , right + 1 , 1 ) : NEW_LINE INDENT arr [ i ] = temp [ i ] NEW_LINE DEDENT return inv_count NEW_LINE DEDENT def _mergeSort ( arr , temp , left , right ) : NEW_LINE INDENT inv_count = 0 NEW_LINE if ( right > left ) : NEW_LINE INDENT mid = int ( ( right + left ) / 2 ) NEW_LINE inv_count = _mergeSort ( arr , temp , left , mid ) NEW_LINE inv_count += _mergeSort ( arr , temp , mid + 1 , right ) NEW_LINE inv_count += merge ( arr , temp , left , mid + 1 , right ) NEW_LINE DEDENT return inv_count NEW_LINE DEDENT def countSwaps ( arr , n ) : NEW_LINE INDENT temp = [ 0 for i in range ( n ) ] NEW_LINE return _mergeSort ( arr , temp , 0 , n - 1 ) NEW_LINE DEDENT if __name__ == ' _ _ main _ _ ' : NEW_LINE INDENT arr = [ 1 , 20 , 6 , 4 , 5 ] NEW_LINE n = len ( arr ) NEW_LINE print ( " Number ▁ of ▁ swaps ▁ is " , countSwaps ( arr , n ) ) NEW_LINE DEDENT