Construct Binary Tree from Inorder and Postorder Traversal

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

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

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        if(inorder.length<=0 && postorder.length<=0) return null;
        return buildCore(inorder,0,inorder.length-1,postorder,0,postorder.length-1);
    }
    public TreeNode buildCore(int[] inorder,int inBegin,int inEnd,int[] postorder,int postBegin,int postEnd){
        int rootVal=postorder[postEnd];
        TreeNode node=new TreeNode(rootVal);
        if(postEnd==postBegin){
            return node;
        }
        
        int inRoot=inBegin;
        while(inorder[inRoot]!=rootVal && inRoot!=inEnd) inRoot++;
        if(inRoot==inEnd && inorder[inRoot]!=rootVal) return null;
        
        int lenLeft=inRoot-inBegin;
        
        if(lenLeft>0){
            node.left=buildCore(inorder,inBegin,inRoot-1,postorder,postBegin,postBegin+lenLeft-1);
        }
        if(inRoot<inEnd){
            node.right=buildCore(inorder,inRoot+1,inEnd,postorder,postBegin+lenLeft,postEnd-1);
        }
        return node;
    }
}