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:    vector<int> inorderTraversal(TreeNode *root)     {        vector<int> result;        TreeNode* p=root;        stack<TreeNode*> s;        while(p!=NULL||!s.empty())        {            if(p!=NULL)            {                s.push(p);                p=p->left;            }            else            {                p=s.top();                result.push_back(p->val);                s.pop();                p=p->right;            }        }                return result;    }};