查找二叉树中和为某一值的路径

struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};
class Solution {
public:
    vector<vector<int> > res;
    vector<int> vec;
    vector<vector<int> > FindPath(TreeNode* root,int expectNumber) {

        if(root==nullptr)  return res;
        vec.push_back(root->val);
        if(expectNumber-root->val==0&&root->left==nullptr&&root->right==nullptr)

        {
            res.push_back(vec);
        }


        FindPath(root->left,expectNumber-root->val);
        FindPath(root->right,expectNumber-root->val);

        if(vec.size()!=0)
            vec.pop_back();     

        return res;
    }


};