LeetCode | Path-Sum

题目描述

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 andsum = 22,

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

return true, as there exist a root-to-leaf path5->4->11->2which sum is 22.

题目意思: 是判断是否有从根节点到叶节点的路径和等于给定的sum值。采用递归实现，具体代码如下！

 1 /**
 2  * Definition for binary tree
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     public boolean hasPathSum(TreeNode root, int sum) {
12         if (root == null) 
13             return false;
14         if (root.left == null && root.right == null && sum == root.val) {
15             return true;
16         }
17         return (hasPathSum(root.left, sum-root.val) || hasPathSum(root.right, sum-root.val));
18     }
19 }