揾到呢個 SO thread。 應該係 algorithm 既 thoery study，但睇黎唔係一個 hard definition 黎過喎。 以小弟淺見，對於你個 `check()` 黎講佢個 algorithm 係自己個 method body。 但係個 method body 除左 recursive calls ...

The Java tutorial Java 101: Classes and objects in Java introduces the fundamentals of Java classes and objects, including how to declare classes, describe attributes via fields, describe behaviors ...