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。