LintCode 二叉树的路径和

样例

给定一个二叉树，和 目标值 = 5:

     1    / \   2   4  / \ 2   3

返回：

[  [1, 2, 2],  [1, 4]]

解法：DFS，注意路径和的概念，要到叶子节点

AC代码：

class Solution {public:    /*     * @param root: the root of binary tree     * @param target: An integer     * @return: all valid paths     */    vector<vector<int>> binaryTreePathSum(TreeNode * root, int target) {        // write your code here        vector<vector<int>> res;        if(!root){            return res;        }        vector<int> a;        TreePathSum(root, target, 0, a, res);        return res;    }    void TreePathSum(TreeNode * root, int target,int now, vector<int>& a, vector<vector<int>> &res) {        // write your code here        now += root->val;        a.push_back(root->val);        if(now == target){            if(!root->right && !root->left )                res.push_back(a);        }        if(root->left){            TreePathSum(root->left, target, now, a, res);            a.pop_back();        }        if(root->right){            TreePathSum(root->right, target, now, a, res);            a.pop_back();        }        return ;    }};