树的子结构

输入两棵二叉树A，B，判断B是不是A的子结构。（ps：我们约定空树不是任意一个树的子结构）

class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}

public class Solution {
    public boolean HasSubtree(TreeNode root1,TreeNode root2) {

        if(root1 == null || root2 == null){
            return  false;
        }
        return check(root1, root2) || HasSubtree(root1.right, root2) || HasSubtree(root1.left, root2);
    }
    public  boolean check(TreeNode root1, TreeNode root2){
        if(root2 == null){
            return true;
        }
        if(root1 == null || root1.val != root2.val){
            return  false;
        }
        return check(root1.left, root2.left) && check(root1.right, root2.right);
    }
}