Leetcode-path-sum

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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.

题意非常简单明确，判断有没有一条从根到叶子节点的路径总和为sum。

代码如下：

 * 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;        sum = sum - root.val;        if(root.left == null && root.right == null && sum == 0)            return true;                if(hasPathSum(root.left, sum))            return true;        if(hasPathSum(root.right, sum))            return true;                return false;    }}

还看到一个代码，思想还是一样，但是更加简洁。

public 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;                return (hasPathSum(root.left, sum-root.val) ||                hasPathSum(root.right, sum-root.val));    }}

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