leetcode中Path Sum 问题

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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.

###问题描述

在二叉树中找到一条路径与sum值相等

###代码如下

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
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;
            } else {
                return false;
            }
        }
        return hasPathSum(root->left,sum-root->val) || hasPathSum(root->right,sum-root->val);
    }
};

简单说明一下，做一个递归函数不断向下递归，直到子节点都为零，判断这个时候的根节点是否等于sum的剩余值