[leetcode 112]Path Sum

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Question:

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：

很容易知道：

1、如果树为NULL，返回false；

2、如果只有根节点一个节点，则比较根节点的值和sum的值即可；

3、如果有子树，则在左右子树中查找有没有总和为 sum - root->val 的路径。

代码：

<span style="font-size:14px;">/** * Definition for a binary tree node. * 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(root->val == sum){                return true;            }            else{                return false;            }        }        return hasPathSum(root->left,sum-root->val) || hasPathSum(root->right,sum-root->val);    }};</span>

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