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.

Solution:

Code:

<span style="font-size:14px;">/** * 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 *helper(const vector<int> &inorder, const vector<int> &postorder, int inBegin, int inEnd, int postBegin, int postEnd) {        if (inBegin > inEnd) return NULL;        TreeNode *root = new TreeNode(postorder[postEnd]);        int index = inBegin;        for (; index <= inEnd; ++index)            if (inorder[index] == postorder[postEnd]) break;        root->left = helper(inorder, postorder, inBegin, index-1, postBegin, index-1-inBegin+postBegin);        root->right = helper(inorder, postorder, index+1, inEnd, index-inBegin+postBegin, postEnd-1);        return root;    }    TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {        return helper(inorder, postorder, 0, inorder.size()-1, 0, postorder.size()-1);    }};</span>