Leetcode: 112. Path Sum(JAVA)

【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.
【思路】

递归实现，当且仅当左右子树都为0时判断val与sum是否相等，否则递归判断左右子树。

【code】

/**
* 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) {
return (root.val == sum);
}else {
return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum-root.val);
}
}
}