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LeetCode-Path Sum II

思路比较简单，在遍历的基础上加入一个变量来跟踪路径即可（记得及时加入和弹出路径）。

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/**
 * 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>> paths;
        if(root==nullptr) return paths;
        vector<int> path;
        helper(root,sum,path,paths);
        return paths;
    }
    void helper(TreeNode* root,int sum,vector<int> &path,vector<vector<int>> &paths){
        if(root==nullptr) return;
        path.push_back(root->val);
        if(root->left==nullptr && root->right==nullptr && sum==root->val){
            vector<int> *tPath=new vector<int>(path);
            paths.push_back(*tPath);
        }
        helper(root->left,sum-root->val,path,paths);
        helper(root->right,sum-root->val,path,paths);
        path.pop_back();
    }
};