comments

solutions/src/2023/07.hs

@@ -8,6 +8,9 @@ Maintainer  : emertens@gmail.com
 
 <https://adventofcode.com/2023/day/7>
 
+Sort the hands of a poker-like card game and compute the
+resulting winnings.
+
 >>> :{
 :main +
 "32T3K 765
@@ -21,11 +24,11 @@ QQQJA 483
 5905
 
 -}
-module Main where
+module Main (main) where
 
 import Advent (format, counts)
-import Data.List (sortOn, sort, elemIndex, nub)
 import Data.Foldable (toList)
+import Data.List (sortOn, sort, elemIndex, nub)
 import Data.Maybe (fromJust)
 
 -- |
@@ -39,16 +42,39 @@ main =
     print (winnings strength1 input)
     print (winnings strength2 input)
 
+-- | Compute the winnings after ordering the given hands by strength
+-- and multiplying the bids by position in the ranked list.
 winnings :: Ord a => (String -> a) -> [(String, Int)] -> Int
 winnings strength input =
   sum [bid * rank | rank        <- [1..]
                   | (hand, bid) <- input, then sortOn by strength hand]
 
+-- | Map a hand to a representative of its strength for part 1
+--
+-- >>> strength1 "2AAAA" < strength1 "33332"
+-- True
+--
+-- >>> strength1 "77788" < strength1 "77888"
+-- True
+--
+-- >>> strength1 "KTJJT" < strength1 "KK677"
+-- True
+--
+-- >>> strength1 "T55J5" < strength1 "QQQJA"
+-- True
 strength1 :: String -> [Int]
 strength1 hand = category hand : map val hand
   where
     val x = fromJust (x `elemIndex` "23456789TJQKA")
 
+-- | Map a hand to a representative of its strength for part 2.
+-- This version treats @J@ as a wildcard of low individual value.
+--
+-- >>> strength2 "JKKK2" < strength2 "QQQQ2"
+-- True
+--
+-- >>> sortOn strength2 ["T55J5", "KTJJT", "QQQJA"]
+-- ["T55J5","QQQJA","KTJJT"]
 strength2 :: String -> [Int]
 strength2 hand =
   maximum
@@ -59,6 +85,7 @@ strength2 hand =
   where
     val x = fromJust (x `elemIndex` "J23456789TQKA")
 
+-- | Map a hand to an integer representing its set size.
 category :: String -> Int
 category hand =
   case sort (toList (counts hand)) of