Scissors Paper Stone and their ordering (Or is it Rock Paper Scissors?)

Inspiration

I was in the bathroom, after watching a video on Kata, and fiddling with the thought of doing a Kata using Haskell. So I thought of what Kata I could try, and figured that a Scissors Paper Stone kata would be cool. I would have a chance to practice IO, hence Monads, and also some simple logic. So that led to the thought of how a game of SPS may work out…

Scissors Paper Stone

Now you probably know the game and how it’s played. Scissors beats Paper, Paper beats Stone, Stone beats Scissors. Hmm what? If we plot how powerful each Move is, we see this:

> Stone
>>> Paper
>>>>> Scissors
>>>>>>> Stone   // what???

This is interesting because, given a list of Scissors, Paper, and Stone, how would the result look like?

Eventually I went to research a bit more, sometimes you just got to know what search terms to type, and I found cyclic ordering. It even classifies Scissors Paper Stone as a Discrete Cycle. But that didn’t stop me from wondering what sorting them will look like!

Code

So I went ahead to explore. Code given is in Java, my most familiar lanugage. Code is ugly because, well its ugly. Maybe I should try to use polymorphism to clean it up… hm… Anyway, the gist is here

static class Move implements Comparable<Move> {
  public enum TYPE {
    SCISSORS, PAPER, STONE
  };

  public static int COUNT = 0;
  private TYPE type;
  private int count;

  private static Move paper() {
    Move move = new Move();
    move.type = TYPE.PAPER;
    move.count = COUNT++;
    return move;
  }

  private static Move scissors() {
    Move move = new Move();
    move.type = TYPE.SCISSORS;
    move.count = COUNT++;
    return move;
  }

  private static Move stone() {
    Move move = new Move();
    move.type = TYPE.STONE;
    move.count = COUNT++;
    return move;
  }

  public String toString() {
    switch (type) {
      case SCISSORS:
        return "Scissors [" + count + "]";
      case PAPER:
        return "Paper [" + count + "]";
      case STONE:
        return "Stone [" + count + "]";
    }
    return "";
  }

  @Override
  public int compareTo(Move o) {
    switch (this.type) {
      case SCISSORS:
        switch (o.type) {
          case SCISSORS:
            return 0;
          case PAPER:
            return 1;
          case STONE:
            return -1;
        }
      case PAPER:
        switch (o.type) {
          case SCISSORS:
            return -1;
          case PAPER:
            return 0;
          case STONE:
            return 1;
        }
      case STONE:
        switch (o.type) {
          case SCISSORS:
            return 1;
          case PAPER:
            return -1;
          case STONE:
            return 0;
        }
  }
  return 0;
  }
}

This is how the Move class looks like, and compareTo basically has the rules for the entire game. After this it was just making an outer class to add Moves to a list and to use Collections.sort on them:

public class ScissorsPaperStone {
  public static void main(String[] args) {
    List<Move> list = new Vector<Move>();

    for (Move move : list) {
      System.out.print(move + ", ");
    }
    System.out.println();

    Collections.sort(list);

    for (Move move : list) {
      System.out.print(move + ", ");
    }
    System.out.println();
    }
}

Results - everything is sorted

The results are as such:

Moves added are: (Scissors-Paper-Stone) 3 times

Original:
Scissors [0], Paper [1], Stone [2], Scissors [3], Paper [4], Stone [5], Scissors [6], Paper [7], Stone [8], 
Sorted:
Stone [8], Paper [7], Scissors [6], Stone [5], Paper [4], Scissors [3], Stone [2], Paper [1], Scissors [0], 

(Scissors-Stone-Paper) 3 times

Original:
Scissors [0], Stone [1], Paper [2], Scissors [3], Stone [4], Paper [5], Scissors [6], Stone [7], Paper [8], 
Sorted:
Scissors [0], Stone [1], Paper [2], Scissors [3], Stone [4], Paper [5], Scissors [6], Stone [7], Paper [8], 

(Stone-Paper-Scissors) 3 times

Original:
Stone [0], Paper [1], Scissors [2], Stone [3], Paper [4], Scissors [5], Stone [6], Paper [7], Scissors [8], 
Sorted:
Stone [0], Paper [1], Scissors [2], Stone [3], Paper [4], Scissors [5], Stone [6], Paper [7], Scissors [8], 

(Stone-Scissors-Paper) 3 times

Original:
Stone [0], Scissors [1], Paper [2], Stone [3], Scissors [4], Paper [5], Stone [6], Scissors [7], Paper [8], 
Sorted:
Paper [8], Scissors [7], Stone [6], Paper [5], Scissors [4], Stone [3], Paper [2], Scissors [1], Stone [0], 

(Paper-Scissors-Stone) 3 times

Original:
Paper [0], Scissors [1], Stone [2], Paper [3], Scissors [4], Stone [5], Paper [6], Scissors [7], Stone [8], 
Sorted:
Paper [0], Scissors [1], Stone [2], Paper [3], Scissors [4], Stone [5], Paper [6], Scissors [7], Stone [8], 

(Paper-Stone-Scissors) 3 times

Original:
Paper [0], Stone [1], Scissors [2], Paper [3], Stone [4], Scissors [5], Paper [6], Stone [7], Scissors [8], 
Sorted:
Scissors [8], Stone [7], Paper [6], Scissors [5], Stone [4], Paper [3], Scissors [2], Stone [1], Paper [0], 

Somewhat random sequence

Original:
Paper [0], Scissors [1], Scissors [2], Stone [3], Paper [4], Stone [5], Paper [6], Scissors [7], Paper [8], Scissors [9], Stone [10], Stone [11], 
Sorted:
Paper [0], Scissors [1], Scissors [2], Scissors [7], Scissors [9], Stone [3], Stone [5], Stone [10], Stone [11], Paper [4], Paper [6], Paper [8], 

Observations?? I don’t really know…

The results are definitely sorted, if we look at them pairwise. For example in the somehwat random sequence, every pair of Moves is sored, but we can see that the 2nd element is Scissors, but the last element is a Paper, and clearly Paper does not beat Scissors.

Another observation is that, sequences that are already sorted don’t change. For example, Paper-Scissors-Stone is already in order, so the whole sequence is sorted, and hence doesn’t change. But I’m not sure how to explain the resuts for the rest, especially for the somewhat random sequence.

But I wanted to know a bit more about how Java does sorting, and so I went to a bit of digging and jotted my discoveries here.