/**

 * Definition for a binary tree node.

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

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

 * };

 */

class Solution {

public:

    ///

    template<typename Iterator>

    TreeNode *help_buildTree_ip(Iterator in_first,Iterator in_last,

        Iterator post_first,Iterator post_last){

        if(in_first == in_last) return nullptr;

        if(post_first == post_last) return nullptr;

        auto val = *prev(post_last);

        TreeNode *root = new TreeNode(val);

        auto in_root_pos = find(in_first,in_last,val);

        auto left_size = distance(in_first,in_root_pos);

        auto post_left_last = next(post_first,left_size);

        root->left = help_buildTree_ip(in_first,in_root_pos,post_first,post_left_last);

        root->right = help_buildTree_ip(next(in_root_pos),in_last,post_left_last,prev(post_last));

        return root;

    }

    TreeNode* buildTree_ip(vector<int> &inorder,vector<int> &postorder){

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

    }

};