Leetcode: Path Sum

Problem:

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.

For 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.

Solution:

Idea:

Pre-order traverse.  DFS.

Code:

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