[LeetCode] Construct Binary Tree from Preorder and Inorder Traversal

/**
 * 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) {
        int len = inorder.size();
        return build(preorder,0,len-1,inorder,0,len-1);
    }
private:
    TreeNode * build(vector<int> &preorder,int begpreorder,int endpreorder,vector<int> &inorder,int begInorder,int endInorder){
        
        if(begInorder>endInorder || begpreorder>endpreorder)
            return NULL;
        
        int val = preorder[begpreorder];
        TreeNode *root = new TreeNode(val);
        if(endInorder==begInorder)
            return root;
        int i,j=0;
        for(i=begInorder;i<=endInorder;i++,j++){
           if(inorder[i]==val)
               break;
        }
            
        root->left = build(preorder,begpreorder+1,begpreorder+j,inorder,begInorder,i-1);
        root->right = build(preorder,begpreorder+1+j,endpreorder,inorder,i+1,endInorder);
        return root;
    
    }
};