AM 1357. Path Sum II

/**
 * 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: a binary tree
     * @param sum: the sum
     * @return: the scheme
     */
    vector<vector<int>> pathSum(TreeNode * root, int sum) {
        // Write your code here.
        vector<vector<int>> res; 
        vector<int> resElem; 
        helper(root, res, resElem, sum); 
        return res; 
    }
    void helper(TreeNode *root, vector<vector<int>> &res, vector<int> &resElem, int sum){
        if(root == NULL){
            return; 
        }
        if(root->left == NULL && root->right == NULL && sum == root->val){
            resElem.push_back(root->val); 
            res.push_back(resElem); 
            resElem.pop_back(); //不能忘记把加入的pop出来啊，回溯里面，只要有push就得用pop，成对出现
            return; 
        }
        resElem.push_back(root->val); 
        helper(root->left, res, resElem, sum - root->val); 
        helper(root->right, res, resElem, sum - root->val); 
        resElem.pop_back(); 
        return; 
    }
};
注意两种写法不同class Solution {
public:
    /**
     * @param root: a binary tree
     * @param sum: the sum
     * @return: the scheme
     */
    vector<vector<int>> pathSum(TreeNode * root, int sum) {
        // Write your code here.
        vector<vector<int>> res; 
        vector<int> resElem; 
        helper(root, res, resElem, sum); 
        return res; 
    }
    void helper(TreeNode *root, vector<vector<int>> &res, vector<int> &resElem, int sum){
        if(root == NULL){
            return; 
        }
        resElem.push_back(root->val); 
        if(root->left == NULL && root->right == NULL && sum == root->val){
            
            res.push_back(resElem); 
            //resElem.pop_back(); 
        }
        //resElem.push_back(root->val); 
        helper(root->left, res, resElem, sum - root->val); 
        helper(root->right, res, resElem, sum - root->val); 
        resElem.pop_back(); 
        return; 
    }
};