Your are given a binary tree in which each node contains a value. Design an algorithm to get all paths which sum to a given value. The path does not need to start or end at the root or a leaf, but it must go in a straight line down.

Have you met this question in a real interview?

Yes

Example

Given a binary tree:

    1
   / \
  2   3
 /   /
4   2

for target =6, return

[
  [2, 4],
  [1, 3, 2]
]

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @param root the root of binary tree
     * @param target an integer
     * @return all valid paths
     */
    vector<vector<int>> binaryTreePathSum2(TreeNode *root, int target) {
        // Write your code here
        vector<vector<int>> res;
        vector<int> buf;
        dfs(root, target, buf, res);
        return res;
    }

    void dfs(TreeNode *root, int target, vector<int> &buf, vector<vector<int>> &res) {
        if (root == NULL)
            return;
        buf.push_back(root->val);
        int sum = 0;
        for (int i = buf.size() - 1; i >= 0; --i) {
            sum += buf[i];
            if (sum == target) {
                vector<int> temp;
                for (int j = i; j < buf.size(); ++j)
                    temp.push_back(buf[j]);
                res.push_back(temp);
            }
        }
        dfs(root->left, target, buf, res);
        dfs(root->right, target, buf, res);
        buf.pop_back();
    }
};