Construct Binary Tree From Inorder and Postorder Traversal

 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 public:
12     TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
13         if(inorder.size() == 0) return NULL;
14         return build(postorder, 0, postorder.size() - 1, inorder, 0, inorder.size() - 1);
15     }
16     TreeNode* build(vector<int>& postorder, int postLeft, int postRight, vector<int>& inorder, int inLeft, int inRight){
17         if(inLeft > inRight) return NULL;
18         
19         TreeNode* root = new TreeNode(postorder[postRight]);
20         if(postLeft == postRight) return root;
21         
22         int index;
23         for(index = 0; index < inorder.size(); index++){
24             if(inorder[index] == root->val) break;
25         }
26         root->left = build(postorder, postLeft, postLeft + index - inLeft - 1, inorder, inLeft, index - 1);
27         root->right = build(postorder, postLeft + index - inLeft, postRight - 1, inorder, index + 1, inRight);
28         
29         return root;
30     }
31 };