This is a skeleton file for your homework.
Complete the functions below.
You may also edit the function "main" to test your code.
You should not use any loops or recursions, except in "delete"
Delete may use one loop or recursive helper.
You must not add fields or static variables.
As always, you must not change the declaration of any method.
Do not change any of the methods I have provided, such as "toString" and "check".