【leetcode】Construct Binary Tree from Inorder and Postorder Traversal

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

 1 class Solution {
 2 public:
 3     TreeNode* createTree(vector<int>& inorder,int instart,int inend,vector<int> &postorder,int poststart,int postend)
 4     {
 5         if(instart>inend) return NULL;
 6
 7         int root=postorder[postend];
 8
 9         int index;
10
11         for(int i=instart;i<=inend;i++)
12         {
13             if(inorder[i]==root)
14             {
15                 index=i;
16                 break;
17             }
18         }
19
20         int len=index-instart;
21         TreeNode *left=createTree(inorder,instart,index-1,postorder,poststart,poststart+len-1);
22         TreeNode *right=createTree(inorder,index+1,inend,postorder,poststart+len,postend-1);
23
24         TreeNode *node=new TreeNode(root);
25         node->left=left;
26         node->right=right;
27
28         return node;
29     }
30     TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
31
32         if(inorder.size()==0) return NULL;
33
34         TreeNode *head=createTree(inorder,0,inorder.size()-1,postorder,0,postorder.size()-1);
35         return head;
36     }
37 };