106. Construct Binary Tree from Inorder and Postorder Traversal

题目：

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

解题思路：

递归

/** * 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:    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {        return buildTree_helper(inorder,0,inorder.size()-1,postorder,0,postorder.size()-1);    }        TreeNode* buildTree_helper(vector<int>& inorder,int start_in,int end_in, vector<int>& postorder,int start_post,int end_post){        if(start_in>end_in)return NULL;        TreeNode* root = new TreeNode(postorder[end_post]);        int i = find(inorder.begin()+start_in,inorder.begin()+end_in,root->val)-inorder.begin()-start_in;        root->left = buildTree_helper(inorder,start_in,start_in+i-1, postorder,start_post,start_post+i-1);        root->right = buildTree_helper(inorder,start_in+i+1,end_in, postorder,start_post+i,end_post-1);        return root;    }};