Path Sum

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.

/** * 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) {        return pathSum(root,sum,0);    }    public boolean pathSum(TreeNode node,int sum,int path){        if(node==null) return false;        if((node.val+path)==sum && node.left==null && node.right==null) return true;        else return pathSum(node.left,sum,node.val+path)||pathSum(node.right,sum,node.val+path);    }}

思路：递归，注意，题目要求，结尾的必须是叶子节点。