113. 路径总和ii

给定一个二叉树和一个目标和，找到所有从根节点到叶子节点路径总和等于给定目标和的路径。

说明: 叶子节点是指没有子节点的节点。

示例: 给定如下二叉树，以及目标和 sum = 22

class Solution {
private:
    void dfs_find(TreeNode* cur,int sum,int targetSum,vector<int> &path,vector<vector<int>> &res)
    {
        path.push_back(cur->val);
        if(cur->left==nullptr && cur->right==nullptr)
        {
            if(sum == targetSum){
                res.push_back(path);
            }
            return;
        }
        if(cur->left){
            dfs_find(cur->left,sum + cur->left->val,targetSum,path,res);
            path.pop_back();
        }
        if(cur->right){
            dfs_find(cur->right,sum + cur->right->val,targetSum,path,res);
            path.pop_back();
        }
    }
public:
    vector<vector<int>> pathSum(TreeNode* root, int targetSum) {
        vector<vector<int>> res;
        vector<int> path;
        if(root==nullptr) return res;
        dfs_find(root,root->val,targetSum,path,res);
        return res;
    }
};