leetcode654 Maximum Binary Tree

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution
11 {
12 public:
13     TreeNode* constructMaximumBinaryTree(vector<int>& nums)
14     {
15         stack<TreeNode*> st;
16         for (auto it: nums)
17         {
18             TreeNode* tmp = new TreeNode(it), *last = NULL;
19             while (!st.empty() && tmp->val > st.top()->val)
20             {
21                 last = st.top(); st.pop();
22             }
23             tmp->left = last;
24             if (!st.empty()) st.top()->right = tmp;
25             st.push(tmp);
26         }
27         TreeNode* res = NULL;
28         while (!st.empty())
29         {
30             res = st.top(); st.pop();
31         }
32         return res;
33     }
34 }