leetcode：Path Sum （途径之和） 【面试算法题】

leetcode：Path Sum （路径之和） 【面试算法题】

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.

              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.

叶子节点就是没有子节点的节点，判断叶子节点的当前值是否等于当前的sum。

若不是叶子节点，将当前sum减去当前节点的值，递归求解。

/** * 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)return false;        if(sum==root->val&&root->left==NULL&&root->right==NULL)return true;        return (root->left && hasPathSum(root->left,sum-root->val) )             ||(root->right && hasPathSum(root->right,sum-root->val));    }};// blog.csdn.net/havenoidea