CareerCup

I dont think it is possible to find a solution in O(n). If it was a pair then yes using a HashMap would help. But if it is more than 2 numbers adding to the sum, its a DP problem and cannot be solved using O(n)

Actually just having the member variables in static is not enough. We need them to be static volatile.

It says create a new BST

public static Node mirrorImage(Node root) {
		if(root == NULL) {
			return;
                }

		  Node n = new Node(root.data);
                n.left = mirrorImage(root.right);
                n.right = mirrorImage(root.left); 
                return n;
          }