Day 10

This code is hilarious

2020/day10/day10.hs

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+import Control.Arrow
+import Control.Monad
+import Data.List
+
+main :: IO ()
+main = do
+  input <- map read . lines <$> readFile "input"
+  print $ (product . map length . group . sort . jolts) input
+  print $
+    (product . map (arrangements . sum) . filter (elem 1) . group . jolts) input
+
+arrangements :: Int -> Int
+arrangements n =
+  length $
+  filter (== n) $ map sum $ nub $ map (filter (/= 0)) $ replicateM n [0 .. 3]
+
+jolts :: [Int] -> [Int]
+jolts =
+  map (uncurry subtract) .
+  ap zip tail .
+  uncurry (++) . (id &&& (flip (:) [] . (+ 3) . last)) . (:) 0 . sort

2020/day10/input

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+99
+3
+1
+11
+48
+113
+131
+43
+82
+19
+4
+153
+105
+52
+56
+109
+27
+119
+147
+31
+34
+13
+129
+17
+61
+10
+29
+24
+12
+104
+152
+103
+80
+116
+79
+73
+21
+133
+44
+18
+74
+112
+136
+30
+146
+100
+39
+130
+91
+124
+70
+115
+81
+28
+151
+2
+122
+87
+143
+62
+7
+126
+95
+75
+20
+123
+63
+125
+53
+45
+141
+14
+67
+69
+60
+114
+57
+142
+150
+42
+78
+132
+66
+88
+140
+139
+106
+38
+85
+37
+51
+94
+98
+86
+68

2020/day10/testinput

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+16
+10
+15
+5
+1
+11
+7
+19
+6
+12
+4

2020/day10/testinput2

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+28
+33
+18
+42
+31
+14
+46
+20
+48
+47
+24
+23
+49
+45
+19
+38
+39
+11
+1
+32
+25
+35
+8
+17
+7
+9
+4
+2
+34
+10
+3