【LeetCode】#112路径总和(Path Sum)

【LeetCode】#112路径总和(Path Sum)

题目描述

给定一个二叉树和一个目标和，判断该树中是否存在根节点到叶子节点的路径，这条路径上所有节点值相加等于目标和。
说明: 叶子节点是指没有子节点的节点。

示例

给定如下二叉树，以及目标和 sum = 22，
5
/
4 8
/ /
11 13 4
/ \
7 2 1
返回 true, 因为存在目标和为 22 的根节点到叶子节点的路径 5->4->11->2。

Description

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.
Note: A leaf is a node with no children.

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.

解法

class Solution {
public boolean hasPathSum(TreeNode root, int sum) {
if(root==null)
return false;
if(root.left==null && root.right==null)
return sum-root.val==0;
return hasPathSum(root.left, sum-root.val) || hasPathSum(root.right, sum-root.val);
}
}