[leetcode] 112. Path Sum

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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.

解法一：

最直接的方法就是recursive函数。如果当前node是leaf，判断value是否等于sum，否则，判断left和right是否是和为sum-root->val的子tree。

/** * 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) return false;                if (!root->left && !root->right)            return (root->val == sum);        else            return hasPathSum(root->left, sum-root->val) ||                hasPathSum(root->right, sum-root->val);    }};

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