LeetCode Binary Tree Inorder Traversal

 1 // 16ms
 2 /**
 3  * Definition for binary tree
 4  * struct TreeNode {
 5  *     int val;
 6  *     TreeNode *left;
 7  *     TreeNode *right;
 8  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 9  * };
10  */
11 class Solution {
12 public:
13     vector<int> inorderTraversal(TreeNode *root) {
14         // Start typing your C/C++ solution below
15         // DO NOT write int main() function
16         stack<TreeNode *> s;
17 
18         vector <int> v;
19         TreeNode *top;
20         if(root==NULL)
21             return v;
22 
23         s.push(root);
24         int f=0;
25         while(!s.empty())
26         {
27             top=s.top();
28             if(top->left&&f==0)
29             {
30                 s.push(top->left);
31             }
32             else
33             {
34                 v.push_back(top->val);
35                 s.pop();
36                 f=1;
37                 if(top->right)
38                 {
39                     s.push(top->right);
40                     f=0;
41                 }
42             }
43         }
44         return v;
45     }
46 };