It's time to code everyone's favorite game!
This is a pretty easy task to do, just throw a bunch of if else statements and you're done, isn't this right?
module Main where
import Data.Char
parseInput :: String -> [(Int, Int)]
parseInput = map (\s -> (ord (s !! 0) - ord 'A', ord (s !! 2) - ord 'X')) . lines
playGame :: [Int] -> [Int] -> Int -> (Int, Int) -> Int
playGame ptsRes ptsAct cyc (p1, p2) = ptsAct !! p2 + cycle ptsRes !! (p1 + cyc * p2)
main = do
input <- parseInput <$> readFile "input"
print $ sum $ map (playgame [3, 0, 6] [1, 2, 3] 2) input
print $ sum $ map (playgame [3, 1, 2] [0, 3, 6] 1) input"WHERE ARE THE IF ELSE? YOU LIAR!"
Don't worry, I will explain everything in due time! Let's start first with the parsing
parseInput :: String -> [(Int, Int)]
parseInput = map (\s -> (ord (s !! 0) - ord 'A', ord (s !! 2) - ord 'X')) . linesPretty straightforward, just split the file into lines, and for each line get a couple of two integers representing each player's move.
Okay, now that the easy part is done, let's tackle the really "what the heck" part
playGame :: [Int] -> [Int] -> Int -> (Int, Int) -> Int
playGame ptsRes ptsAct cyc (p1, p2) = ptsAct !! p2 + cycle ptsRes !! (p1 + cyc * p2)"What the heck is going on here"
Well here is how everything works. Let us start with the easy part:
ptsAct is the list of points that are linked to the action I perform. That is for part1 "If I play rock I get 1 point, paper 2 points and scissors 3 points", and for part2 "If I lose I get 0 points, draw 3 points and win 6 points". Hence this code in the main function:
print $ sum $ map (playgame [3, 0, 6] [1, 2, 3] 2) input -- Notice the [1, 2, 3]
print $ sum $ map (playgame [3, 1, 2] [0, 3, 6] 1) input -- Notice the [0, 3, 6]ptsRes is a little bit harder to understand. It is the list of points that are linked to how the action I perform is related to the action my opponent performs. That is in part1 things likes "If I play rock and my opponent plays scissors, then I win so I get 6 points", and for part2 "If I want to lose and my opponent plays rock then I play scissors and get 3 points".
Now the weird thing is "If this list is supposed to represent some kind of relation between these two actions, then why is it a list of three values and not a matrix of 3x3?"
Glad you asked! ❤️ It all becomes clearer if we create said matrices:
| 0 | 1 | 2 | |
|---|---|---|---|
| 0 | 3 | 6 | 0 |
| 1 | 0 | 3 | 6 |
| 2 | 6 | 0 | 3 |
| 0 | 1 | 2 | |
|---|---|---|---|
| 0 | 3 | 1 | 2 |
| 1 | 1 | 2 | 3 |
| 2 | 2 | 3 | 1 |
Notice how each line/column is just the same shifted by some amount?
Well this offset is exactly was the cyc parameter is all about! (cyc for cycle you see!) So basically, each time I ask for a specific column, I shift everything by that offset, and because I'm using cycle I don't even need to use any modulo, and it works for both parts!
Then the main function is pretty straightforward: just parse the input, get the result for each game, sum the scores and print it!