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#include <iostream>
#include <algorithm>
#include <vector>


/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/

using std::vector;
using std::find;

struct TreeNode
{
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Solution
{
private:
    TreeNode* buildTree(vector<int>::iterator PostBegin, vector<int>::iterator PostEnd,
                        vector<int>::iterator InBegin, vector<int>::iterator InEnd)
    {
        if (InBegin == InEnd)
        {
            return NULL;
        }

        if (PostBegin == PostEnd)
        {
            return NULL;
        }

        int HeadValue = *(--PostEnd);
        TreeNode *HeadNode = new TreeNode(HeadValue);

        vector<int>::iterator LeftEnd = find(InBegin, InEnd, HeadValue);
        if (LeftEnd != InEnd)
        {
            HeadNode->left = buildTree(PostBegin, PostBegin + (LeftEnd - InBegin),
                             InBegin, LeftEnd);
        }

        HeadNode->right = buildTree(PostBegin + (LeftEnd - InBegin), PostEnd,
                                LeftEnd + 1, InEnd);

        return HeadNode;
    }
public:
    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder)
    {
        if (inorder.empty())
        {
            return NULL;
        }

        return buildTree(postorder.begin(), postorder.end(), inorder.begin(),
                         inorder.end());

    }
};

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