leetcode-Construct Binary Tree from Preorder and Inorder Traversal

Given preorder and inorder traversal of a tree, construct the binary 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 *build(vector<int>&pre,int prestart,int preend,vector<int>&in,int instart,int inend)    {        if(preend<prestart||inend<instart||(preend-prestart)!=(inend-instart))            return NULL;        TreeNode *head = new TreeNode(pre[prestart]);        int rootpos;        for(int i=0;i<=inend-instart;i++)            if(in[i+instart]==pre[prestart])            {                rootpos = i;                break;            }                    head->left = build(pre,prestart+1,prestart+rootpos,in,instart,instart+rootpos-1);        head->right = build(pre,prestart+rootpos+1,preend,in,instart+rootpos+1,inend);        return head;    }    TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder)     {        int presize = preorder.size();        int insize   = inorder.size();        TreeNode *head = build(preorder,0,presize-1,inorder,0,insize-1);        return head;    }};