Leetcode -- Construct Binary Tree from Inorder and Postorder 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:  
   TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {  
     if(inorder.empty() || postorder.empty()) {  
       return NULL;  
     }  
     return buildTree(inorder, 0, inorder.size() - 1, postorder, 0, postorder.size() - 1);  
   }  
   TreeNode * buildTree(vector<int>& inorder, int iStart, int iEnd, vector<int>& postorder, int pStart, int pEnd) {  
     if(iStart > iEnd || pStart > pEnd) {  
       return NULL;  
     }  
     TreeNode * root = new TreeNode (postorder[pEnd]);  
     int i = iStart;  
     for(; i <= iEnd; ++i) {  
       if(inorder[i] == postorder[pEnd]) {  
         break;  
       }  
     }  
     root->left = buildTree(inorder, iStart, i - 1, postorder, pStart, pStart + i - iStart - 1);  
     root->right = buildTree(inorder, i + 1, iEnd, postorder, pEnd + i - iEnd, pEnd - 1);  
     return root;  
   }  
 };