[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.

/**
 * 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) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        return build(inorder,0,inorder.size()-1,postorder,0,postorder.size()-1);
    }
    
    
    TreeNode *build(vector<int> &inorder,int iStart, int iEnd, vector<int> &postorder, int pStart, int pEnd) {
        if(iStart > iEnd) return NULL;
        if(iStart == iEnd) return new TreeNode(inorder[iStart]);
        
        TreeNode *root = new TreeNode(postorder[pEnd]);
        
        int index = iStart;
        while(index <= iEnd && inorder[index] != postorder[pEnd]) index++;
        
        int leftLen = index-iStart;
        root->left = build(inorder,iStart,index-1,postorder,pStart,pStart+leftLen-1);
        root->right = build(inorder,index+1,iEnd,postorder,pStart+leftLen,pEnd-1);
        return root;
        
    }
};