Construct Binary Tree from Preorder and Inorder Traversal

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

Note:
You may assume that duplicates do not exist in the 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 *buildTree(vector<int> &preorder, vector<int> &inorder) 

    {

        return buildTree(preorder,0,preorder.size()-1,inorder,0,inorder.size()-1);

    }

    TreeNode *buildTree(const vector<int> &preorder,int pl,int pr,const vector<int> &inorder,int il,int ir)

    {

        if(pl>pr) return NULL;

        TreeNode* root=new TreeNode(preorder[pl]);

        int mid=il;

        while(inorder[mid]!=root->val) mid++;

        root->left=buildTree(preorder,pl+1,pl+mid-il,inorder,il,mid-1);

        root->right=buildTree(preorder,pr+1-(ir-mid),pr,inorder,mid+1,ir);

    }

};