Leetcode112 Path Sum

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

样例

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

本题是考察遍历的一种方式，要注意的点包括：
1、没说不能是负数
2、空树的时候应当返回的值
3、同时满足和为sum和root-to-leaf path的条件，要注意root-to-leaf path的判定

因为一定要遍历到叶子节点，所以写清楚叶子节点的递归终止情况就行了。

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

感觉糟糕的时候需要再来一瓶。