Rock-paper-scissors
In this task, the goal is to implement the classic children's game Rock-paper-scissors, as well as a simple predictive AI player.
Rock Paper Scissors has two players. Each player chooses one of rock, paper or scissors, without knowing the other player's choice. The winner is decided by a set of rules:
- Rock beats scissors
- Scissors beat paper
- Paper beats rock.
If both players choose the same thing, there is no winner for that round.
For this task's AI player, keep track of the player's choice frequency, and use that choice frequency to make a weighted random choice to beat the player's likely choice.
Ada
<lang Ada>with Ada.Text_IO; with Ada.Numerics.Float_Random;
procedure Rock_Paper_Scissors is
package Rand renames Ada.Numerics.Float_Random; Gen: Rand.Generator;
type Choice is (Rock, Paper, Scissors);
Cnt: array (Choice) of Natural := (1, 1, 1);
-- for the initialization: pretend that each of Rock, Paper,
-- and Scissors, has been played once by the human
-- else the first computer choice would be deterministic
function Computer_Choice return Choice is
Random_Number: Natural :=
Integer(Rand.Random(Gen)
* (Float(Cnt(Rock)) + Float(Cnt(Paper)) + Float(Cnt(Scissors))));
begin
if Random_Number < Cnt(Rock) then
-- guess the human will choose Rock
return Paper;
elsif Random_Number - Cnt(Rock) < Cnt(Paper) then
-- guess the human will choose Paper
return Scissors;
else -- guess the human will choose Scissors
return Rock;
end if;
end Computer_Choice;
Finish_The_Game: exception;
function Human_Choice return Choice is
Done: Boolean := False;
T: constant String
:= "enter ""r"" for Rock, ""p"" for Paper, or ""s"" for Scissors""!";
U: constant String
:= "or enter ""q"" to Quit the game";
Result: Choice;
begin
Ada.Text_IO.Put_Line(T);
Ada.Text_IO.Put_Line(U);
while not Done loop
Done := True;
declare
S: String := Ada.Text_IO.Get_Line;
begin
if S="r" or S="R" then
Result := Rock;
elsif S="p" or S = "P" then
Result := Paper;
elsif S="s" or S="S" then
Result := Scissors;
elsif S="q" or S="Q" then
raise Finish_The_Game;
else
Done := False;
end if;
end;
end loop;
return Result;
end Human_Choice;
type Result is (Human_Wins, Draw, Computer_Wins);
function "<" (X, Y: Choice) return Boolean is
-- X < Y if X looses against Y
begin
case X is
when Rock => return (Y = Paper);
when Paper => return (Y = Scissors);
when Scissors => return (Y = Rock);
end case;
end "<";
Score: array(Result) of Natural := (0, 0, 0);
C,H: Choice;
Res: Result;
begin
-- play the game
loop
C := Computer_Choice; -- the computer makes its choice first
H := Human_Choice; -- now ask the player for his/her choice
Cnt(H) := Cnt(H) + 1; -- update the counts for the AI
if C < H then
Res := Human_Wins;
elsif H < C then
Res := Computer_Wins;
else
Res := Draw;
end if;
Ada.Text_IO.Put_Line("COMPUTER'S CHOICE: " & Choice'Image(C)
& " RESULT: " & Result'Image(Res));
Ada.Text_IO.New_Line;
Score(Res) := Score(Res) + 1;
end loop;
exception
when Finish_The_Game =>
Ada.Text_IO.New_Line;
for R in Score'Range loop
Ada.Text_IO.Put_Line(Result'Image(R) & Natural'Image(Score(R)));
end loop;
end Rock_Paper_Scissors;</lang>
First and last few lines of the output of a game, where the human did permanently choose Rock:
./rock_paper_scissors enter "r" for Rock, "p" for Paper, or "s" for Scissors"! or enter "q" to Quit the game r COMPUTER'S CHOICE: SCISSORS RESULT: HUMAN_WINS enter "r" for Rock, "p" for Paper, or "s" for Scissors"! or enter "q" to Quit the game r COMPUTER'S CHOICE: ROCK RESULT: DRAW enter "r" for Rock, "p" for Paper, or "s" for Scissors"! or enter "q" to Quit the game r COMPUTER'S CHOICE: SCISSORS RESULT: HUMAN_WINS enter "r" for Rock, "p" for Paper, or "s" for Scissors"! or enter "q" to Quit the game r COMPUTER'S CHOICE: ROCK RESULT: DRAW [...] enter "r" for Rock, "p" for Paper, or "s" for Scissors"! or enter "q" to Quit the game r COMPUTER'S CHOICE: ROCK RESULT: DRAW enter "r" for Rock, "p" for Paper, or "s" for Scissors"! or enter "q" to Quit the game r COMPUTER'S CHOICE: PAPER RESULT: COMPUTER_WINS enter "r" for Rock, "p" for Paper, or "s" for Scissors"! or enter "q" to Quit the game q HUMAN_WINS 2 DRAW 5 COMPUTER_WINS 21
C
<lang C>#include <stdio.h>
- include <stdlib.h>
int rand_i(int n) { int rand_max = RAND_MAX - (RAND_MAX % n); int ret; while ((ret = rand()) >= rand_max); return ret/(rand_max / n); }
int weighed_rand(int *tbl, int len) { int i, sum, r; for (i = 0, sum = 0; i < len; sum += tbl[i++]); if (!sum) return rand_i(len);
r = rand_i(sum) + 1; for (i = 0; i < len && (r -= tbl[i]) > 0; i++); return i; }
int main() { int user_action, my_action; int user_rec[] = {0, 0, 0}; char *names[] = { "Rock", "Paper", "Scissors" }; char str[2]; char *winner[] = { "We tied.", "Meself winned.", "You win." };
while (1) { my_action = (weighed_rand(user_rec, 3) + 1) % 3;
printf("\nYour choice [1-3]:\n" " 1. Rock\n 2. Paper\n 3. Scissors\n> ");
/* scanf is a terrible way to do input. should use stty and keystrokes */ if (!scanf("%d", &user_action)) { scanf("%1s", str); if (*str == 'q') return 0; continue; } user_action --; if (user_action > 2 || user_action < 0) { printf("invalid choice; again\n"); continue; } printf("You chose %s; I chose %s. %s\n", names[user_action], names[my_action], winner[(my_action - user_action + 3) % 3]);
user_rec[user_action]++; } }</lang>
Java
This could probably be made simpler, but some more complexity is necessary so that other items besides rock, paper, and scissors can be added (as school children like to do). The method getAIChoice() borrows from the Ada example in spirit, but is more generic to additional items.
<lang java5>import java.util.EnumMap;
import java.util.Map;
import java.util.Scanner;
public class RPS { public enum Item{ ROCK, PAPER, SCISSORS; //add other throwable items here if you wish } //EnumMap uses a simple array under the hood public static Map<Item, Item> beats = new EnumMap<Item, Item>(Item.class){{ put(Item.ROCK, Item.SCISSORS); put(Item.PAPER, Item.ROCK); put(Item.SCISSORS, Item.PAPER); //add other rules here for additional types }};
public static Map<Item, Item> losesTo = new EnumMap<Item, Item>(Item.class){{ put(Item.SCISSORS, Item.ROCK); put(Item.ROCK, Item.PAPER); put(Item.PAPER, Item.SCISSORS); //add other rules here for additional types }};
public static Map<Item, Integer> counts = new EnumMap<Item, Integer>(Item.class){{ put(Item.ROCK, 1); put(Item.PAPER, 1); put(Item.SCISSORS, 1); //add other counts here for additional types }};
private static int totalThrows = Item.values().length;
public static void main(String[] args){ Scanner in = new Scanner(System.in); System.out.print("Make your choice: "); while(in.hasNextLine()){ Item aiChoice = getAIChoice(); String input = in.nextLine(); Item choice; try{ choice = Item.valueOf(input.toUpperCase()); }catch (IllegalArgumentException ex){ System.out.println("Invalid choice"); continue; } counts.put(choice, counts.get(choice) + 1); totalThrows++; System.out.println("Computer chose: " + aiChoice); if(aiChoice.equals(choice)){ System.out.println("Tie!"); }else if(beats.get(choice).equals(aiChoice)){ System.out.println("You chose...wisely. You win!"); }else{ System.out.println("You chose...poorly. You lose!"); } System.out.print("Make your choice: "); } }
private static Item getAIChoice() { int rand = (int)(Math.random() * (totalThrows)); for(Item item:Item.values()){ if(rand < counts.get(item)){ return losesTo.get(item); } rand -= counts.get(item); } return null; } }</lang> Sample output:
Make your choice: rock Computer chose: PAPER You chose...poorly. You lose! Make your choice: rock Computer chose: SCISSORS You chose...wisely. You win! Make your choice: rock Computer chose: PAPER You chose...poorly. You lose! Make your choice: rock Computer chose: SCISSORS You chose...wisely. You win! Make your choice: rock Computer chose: PAPER You chose...poorly. You lose! Make your choice: rock Computer chose: ROCK Tie! Make your choice: rock Computer chose: ROCK Tie! Make your choice: rock Computer chose: PAPER You chose...poorly. You lose! Make your choice: rock Computer chose: PAPER You chose...poorly. You lose! Make your choice: rock Computer chose: PAPER You chose...poorly. You lose! Make your choice: scissors Computer chose: PAPER You chose...wisely. You win! Make your choice: scissors Computer chose: PAPER You chose...wisely. You win! ...
Python
<lang python>#!/usr/bin/python from random import randint, random from operator import add from functools import reduce from bisect import bisect_left
WHATBEATS = { 'paper' : 'scissors',
'scissors' : 'rock',
'rock' : 'paper' }
ORDER = ('rock', 'paper', 'scissors')
CHOICEFREQUENCY = {}
def probChoice(choices, probabilities):
scalefactor = reduce(add, probabilities)
prob_accumulator = 0
accumulator = []
for p in probabilities:
prob_accumulator += float(p) / scalefactor
accumulator.append(prob_accumulator)
r = random()
bsct = bisect_left(accumulator, r)
chc = choices[bsct]
return chc
def checkWinner(a, b):
global WHATBEATS
abeater = WHATBEATS[a] bbeater = WHATBEATS[b]
if b == abeater:
return b
elif a == bbeater:
return a
return None
def sanitizeChoice(a):
# Drop it to lower-case return a.lower()
def registerPlayerChoice(choice):
global CHOICEFREQUENCY
if choice in CHOICEFREQUENCY:
CHOICEFREQUENCY[choice] += 1
else:
CHOICEFREQUENCY[choice] = 1
def getRandomChoice():
global WHATBEATS
global ORDER
global CHOICEFREQUENCY
if len(CHOICEFREQUENCY.keys()) == 0:
return ORDER[randint(0,len(ORDER)-1)]
choices = CHOICEFREQUENCY.keys()
probabilities = CHOICEFREQUENCY.values()
return WHATBEATS[probChoice(choices, probabilities)]
while True:
choice = raw_input()
choice = sanitizeChoice(choice)
if not choice in ORDER:
continue
compChoice = getRandomChoice() print "Computer picked", compChoice+",",
# Don't register the player choice until after the computer has made # its choice. registerPlayerChoice(choice)
winner = checkWinner(choice, compChoice)
if winner == None:
winner = "nobody"
print winner, "wins!"</lang>
Output, where player always chooses Rock:
!504 #5 j0 ?0 $ ./rps.py rock Computer picked scissors, rock wins! rock Computer picked paper, paper wins! rock Computer picked paper, paper wins! rock Computer picked paper, paper wins! rock Computer picked paper, paper wins!