leetcode：Path Sum 【Java】

一、问题描述

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.
二、问题分析

利用递归思想。

三、算法代码

/**
 * Definition for a binary tree node.
 * 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 (root.left == null && root.right == null){ // leaf
            return sum == root.val;
        }
        return hasPathSum(root.left, sum - root.val)
        || hasPathSum(root.right, sum - root.val);
    }
}