Day_01(2023): solved

2023/Day_01/Day_01.hs

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+module Main where
+
+import Data.Char
+import Data.List
+import System.Environment
+
+type Input = [String]
+type Output = Int
+
+parseInput :: String -> Input
+parseInput = lines
+
+partOne :: Input -> Output
+partOne = sum . map (\s -> read $ [head s, last s] ) . map (filter isDigit)
+
+partTwo :: Input -> Output
+partTwo = partOne . map go
+    where go "" = ""
+          go line@(c : xs)
+            | "one"   `isPrefixOf` line = '1' : go xs
+            | "two"   `isPrefixOf` line = '2' : go xs
+            | "three" `isPrefixOf` line = '3' : go xs
+            | "four"  `isPrefixOf` line = '4' : go xs
+            | "five"  `isPrefixOf` line = '5' : go xs
+            | "six"   `isPrefixOf` line = '6' : go xs
+            | "seven" `isPrefixOf` line = '7' : go xs
+            | "eight" `isPrefixOf` line = '8' : go xs
+            | "nine"  `isPrefixOf` line = '9' : go xs
+            | otherwise                 =  c  : go xs
+
+compute :: Input -> String -> IO ()
+compute input "parse" = print input
+compute input "one"   = print . partOne $ input
+compute input "two"   = print . partTwo $ input
+compute input _       = error "Unknown part"
+
+main = do
+    args  <- getArgs
+    input <- parseInput <$> (readFile $ last args)
+    mapM (compute input)  $ init args

2023/Day_01/README.md

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+## Day 01
+
+Let's talk a little bit about me first, shall we?
+
+This is my fourth time doing this in Haskell. Last year was the first time
+I managed to solve all days, so I thought I might stop doing thoses in Haskell
+as I felt like I had accomplished everything I ought to do with this language.
+
+But after thinking for a while, looking for a challenge that would make me happy,
+I realised that this small period of the year where I do Haskell is probably my favorite time
+of the year. Thus, I've decided once again to solve thoses in Haskell!
+
+TL;DR: Hello, my name is Sheinxy and I'm that weird Haskell guy! 🐈‍⬛
+
+Anyway, let's start with the challenge. For this year, I've decided to make a small
+shell script to generate some boilerplate code to make things faster (let's see
+how long I use this until I find it not specific enough for each problem):
+
+```hs
+module Main where
+
+import Data.Char
+import Data.List
+import System.Environment
+
+type Input = [String]
+type Output = Int
+
+parseInput :: String -> Input
+parseInput = lines
+
+partOne :: Input -> Output
+partOne = sum . map (\s -> read $ [head s, last s] ) . map (filter isDigit)
+
+partTwo :: Input -> Output
+partTwo = partOne . map go
+    where go "" = ""
+          go line@(c : xs)
+            | "one"   `isPrefixOf` line = '1' : go xs
+            | "two"   `isPrefixOf` line = '2' : go xs
+            | "three" `isPrefixOf` line = '3' : go xs
+            | "four"  `isPrefixOf` line = '4' : go xs
+            | "five"  `isPrefixOf` line = '5' : go xs
+            | "six"   `isPrefixOf` line = '6' : go xs
+            | "seven" `isPrefixOf` line = '7' : go xs
+            | "eight" `isPrefixOf` line = '8' : go xs
+            | "nine"  `isPrefixOf` line = '9' : go xs
+            | otherwise                 =  c  : go xs
+
+compute :: Input -> String -> IO ()
+compute input "parse" = print input
+compute input "one"   = print . partOne $ input
+compute input "two"   = print . partTwo $ input
+compute input _       = error "Unknown part"
+
+main = do
+    args  <- getArgs
+    input <- parseInput <$> (readFile $ last args)
+    mapM (compute input)  $ init args
+```
+
+Okay, that makes the code quite long actually, so from now on I'm only going to focus
+on the parseInput, partOne and partTwo functions.
+
+```hs
+type Input = [String]
+type Output = Int
+
+parseInput :: String -> Input
+parseInput = lines
+
+partOne :: Input -> Output
+partOne = sum . map (\s -> read $ [head s, last s] ) . map (filter isDigit)
+
+partTwo :: Input -> Output
+partTwo = partOne . map go
+    where go "" = ""
+          go line@(c : xs)
+            | "one"   `isPrefixOf` line = '1' : go xs
+            | "two"   `isPrefixOf` line = '2' : go xs
+            | "three" `isPrefixOf` line = '3' : go xs
+            | "four"  `isPrefixOf` line = '4' : go xs
+            | "five"  `isPrefixOf` line = '5' : go xs
+            | "six"   `isPrefixOf` line = '6' : go xs
+            | "seven" `isPrefixOf` line = '7' : go xs
+            | "eight" `isPrefixOf` line = '8' : go xs
+            | "nine"  `isPrefixOf` line = '9' : go xs
+            | otherwise                 =  c  : go xs
+```
+
+Okay that is already less scary :3c
+
+Parsing the input is just spliting the file line by line, nothing too fancy.
+My input is therefore a list of lines, and my output is a number.
+
+
+Let's focus on part one first:
+```hs
+partOne = sum . map (\s -> read $ [head s, last s] ) . map (filter isDigit)
+```
+
+I start by removing anything that is not a digit from the line, then I keep the first and last digit and convert them to an int.
+I sum every line result together, and I'm done! That is not the most optimised (nor probably the most elegant), but it's simple enough in my opinion.
+
+Then, part two:
+```hs
+partTwo = partOne . map go
+    where go "" = ""
+          go line@(c : xs)
+            | "one"   `isPrefixOf` line = '1' : go xs
+            | "two"   `isPrefixOf` line = '2' : go xs
+            | "three" `isPrefixOf` line = '3' : go xs
+            | "four"  `isPrefixOf` line = '4' : go xs
+            | "five"  `isPrefixOf` line = '5' : go xs
+            | "six"   `isPrefixOf` line = '6' : go xs
+            | "seven" `isPrefixOf` line = '7' : go xs
+            | "eight" `isPrefixOf` line = '8' : go xs
+            | "nine"  `isPrefixOf` line = '9' : go xs
+            | otherwise                 =  c  : go xs
+```
+
+Basically part two starts by "reparsing" the input before doing exactly what part one does.
+The reparsing simply changes every number written in letter form as the same number in digit form.
+
+The only small problem that I had with part 2 was that "oneight" is actually "18" and not "1ight",
+so I cannot drop the whole "one" from the string (I was too lazy to check what can be a prefix of what to be optimise, so I simply drop the first letter)
+
+That's all for today folks!