Binary Tree Inorder Traversal

/**
 * 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;
    }
};