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;
    }
};