树的子结构

题目描述：输入两颗二叉树A，B，判断B是不是A的子结构。

    public static boolean HasSubtree(TreeNode root1, TreeNode root2) {
        if(root1 == null || root2 == null){
            return false;
        }
        return isSubtree(root1, root2) || isSubtree(root1.left, root2) ||isSubtree(root1.right, root2);
    }
    public static boolean isSubtree(TreeNode t1, TreeNode t2){
        if(t2 == null){
            return true;
        }
        if(t1 == null){
            return false;
        }
        return (t1.val == t2.val)&& isSubtree(t1.left, t2.left) && isSubtree(t1.right, t2.right);
    }