113. Path Sum II

Given a binary tree and a sum, find all root-to-leaf paths where each path’s sum equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5             / \            4   8           /   / \          11  13  4         /  \    / \        7    2  5   1

return

[   [5,4,11,2],   [5,8,4,5]]

/** * 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:    vector<vector<int>> res;    void dfs(TreeNode* root, int sum, vector<int>& vec, int s){        if(root == NULL) return ;        if(root->left == NULL && root->right == NULL){            s += root->val;            vec.push_back(root->val);            if(s == sum){                res.push_back(vec);            }            vec.pop_back();            return ;        }         vec.push_back(root->val);        dfs(root->left, sum, vec, s + root->val);        dfs(root->right, sum, vec, s + root->val);        vec.pop_back();    }    vector<vector<int>> pathSum(TreeNode* root, int sum) {        if(root == NULL) return vector<vector<int>>();        vector<int> vec;        dfs(root, sum, vec, 0);        return res;    }};