We make two recursive calls , so reduce k by 2.
k -= 2 ; int mid = ( l + r ) / 2 ; int temp = a [ mid - 1 ] ; a [ mid - 1 ] = a [ mid ] ; a [ mid ] = temp ; unsort ( l , mid , a , k ) ; unsort ( mid , r , a , k ) ; } static void arrayWithKCalls ( int n , int k ) { if ( k % 2 == 0 ) { Console . WriteLine ( " NO ▁ SOLUTION " ) ; return ; }