/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    void InOrder(TreeNode *root,vector<int>&vec)    {        if(root==NULL) return ;        InOrder(root->left,vec);        vec.push_back(root->val);        InOrder(root->right,vec);    }    vector<int> inorderTraversal(TreeNode *root) {        vector<int>vec;        InOrder(root,vec);        return vec;    }};