112- Path Sum

题目

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.

分析

思路1：
递归求解

思路2
利用后序遍历

实现

class Solution {public:    bool hasPathSum(TreeNode *root, int sum)    {        if (!root)            return false;        if (root->val == sum&& !root->left&& !root->right)            return true;        return hasPathSum(root->left, sum - root->val) ||  hasPathSum(root->right, sum - root->val);    }};