Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

5     / \    4   8   /   / \  11  13  4 /  \      \7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

 

time: O(n), space: O(height)

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */class Solution {    public boolean hasPathSum(TreeNode root, int sum) {        if(root == null) {            return false;        }        if(root.left == null && root.right == null) {            return sum - root.val == 0;        }        return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val);    }}