113. Path Sum II

Typical DFS problem. I was trying to prune the algorithm but it turns out I don't have to. The code is much concise without pruning and the performance isn't bad (16ms)

1:  /**  
2:   * Definition for a binary tree node.  
3:   * struct TreeNode {  
4:   *   int val;  
5:   *   TreeNode *left;  
6:   *   TreeNode *right;  
7:   *   TreeNode(int x) : val(x), left(NULL), right(NULL) {}  
8:   * };  
9:   */  
10:  class Solution {  
11:  public:  
12:    vector<vector<int>> pathSum(TreeNode* root, int sum) {  
13:      vector<vector<int>> res;  
14:      vector<int> sol;  
15:      helper(root, sum, sol, res);  
16:      return res;  
17:    }  
18:    void helper(TreeNode *root, int sum, vector<int> &sol, vector<vector<int>> &res) {  
19:      if (root == NULL) return;  
20:      sol.push_back(root->val);  
21:      if (!root->left && !root->right && sum == root->val)  
22:        res.push_back(sol);  
23:      helper(root->left, sum-root->val, sol, res);  
24:      helper(root->right, sum-root->val, sol, res);  
25:      sol.pop_back();  
26:      return;  
27:    }  
28:  };