113. Path Sum II.cpp

/**
 * 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>> pathSum(TreeNode* root, int sum) {
        vector<vector<int>>res;
        if(!root) return res;
        DFS(root, res, vector<int>(), 0, sum);
        return res;
    }
    
    void DFS(TreeNode* root, vector<vector<int>>& res, vector<int>path, int sum, int target){
        if(!root) return;
        path.push_back(root->val);
        sum += root->val;
        if(!root->left && !root->right){
            if(sum == target) res.push_back(path);
            return;
        }
        DFS(root->left, res, path, sum, target);
        DFS(root->right, res, path, sum, target);
    }
};