[Amazon interview Question] Calculate the weight of of binary tree path from root to leaf node in such a way that it would be equal to N

You have a binary tree (no BST etc, a simple binary tree). A number N will be given to you, you have to find out, whether path from root node to leaf node exists in such a way so that sum of all node's data in that path is equal to N. For example for given binary tree

           1

     2              3

 4       5      6           7

      3                           8
                             9

If value of N is 11 then path - 1 2 5 3 which is root node to left node 3 sums up to 11 hence for this tree method should return true.
Constraints: Time complexity is O(n) and space complexity should be O(1)
Method to implement : public boolean isSumTree(Node root, int N);

static class Node{
        int data;
        Node left;
        Node right;
    }
    public static boolean isSumTree(Node root, int N){
        if (root.left == null && root.right == null ){
            return root.data == N;
        }
        boolean leftResult = root.left != null && isSumTree(root.left, N - root.data );
        boolean rightResult = root.right != null && isSumTree(root.right, N - root.data );
        return leftResult || rightResult;
    }

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