LeetCode 112. Path Sum(路径和)

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原题网址:https://leetcode.com/problems/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.

方法:递归,自底向上。

/** * 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;        if (root.left != null && hasPathSum(root.left, sum - root.val)) return true;        if (root.right != null && hasPathSum(root.right, sum - root.val)) return true;        return false;    }}

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