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Day 21

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RhiobeT Chan
2023-12-21 15:40:21 +01:00
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module Part2 where
import Commons
import Data.Array (assocs, bounds, (//))
getReachableOdd :: Garden -> Int
getReachableOdd garden =
let ((yMin, xMin), (yMax, xMax)) = bounds garden
n = (yMax - yMin + div (yMax - yMin) 2)
newGarden = garden // [((1 + div (yMax - yMin) 2, 1 + div (xMax - xMin) 2), Plot {reachable = True})]
in length $ getReachableAfterNMove n newGarden
getReachableEven :: Garden -> Int
getReachableEven garden =
let ((yMin, xMin), (yMax, xMax)) = bounds garden
n = (yMax - yMin + 1 + div (yMax - yMin) 2)
newGarden = garden // [((1 + div (yMax - yMin) 2, 1 + div (xMax - xMin) 2), Plot {reachable = True})]
in length $ getReachableAfterNMove n newGarden
getReachableCardinals :: Garden -> [Int]
getReachableCardinals garden =
let ((yMin, xMin), (yMax, xMax)) = bounds garden
n = yMax - yMin
(yMean, xMean) = (1 + div (yMax - yMin) 2, 1 + div (xMax - xMin) 2)
in [length $ getReachableAfterNMove n $ garden // [((yMean, xMin), Plot {reachable = True})],
length $ getReachableAfterNMove n $ garden // [((yMean, xMax), Plot {reachable = True})],
length $ getReachableAfterNMove n $ garden // [((yMin, xMean), Plot {reachable = True})],
length $ getReachableAfterNMove n $ garden // [((yMax, xMean), Plot {reachable = True})]]
getReachableOddCorners :: Garden -> [Int]
getReachableOddCorners garden =
let ((yMin, xMin), (yMax, xMax)) = bounds garden
n = yMax - yMin + div (yMax - yMin) 2
in [length $ getReachableAfterNMove n $ garden // [((yMin, xMin), Plot {reachable = True})],
length $ getReachableAfterNMove n $ garden // [((yMin, xMax), Plot {reachable = True})],
length $ getReachableAfterNMove n $ garden // [((yMax, xMin), Plot {reachable = True})],
length $ getReachableAfterNMove n $ garden // [((yMax, xMax), Plot {reachable = True})]]
getReachableEvenCorners :: Garden -> [Int]
getReachableEvenCorners garden =
let ((yMin, xMin), (yMax, xMax)) = bounds garden
n = div (yMax - yMin) 2 - 1
in [length $ getReachableAfterNMove n $ garden // [((yMin, xMin), Plot {reachable = True})],
length $ getReachableAfterNMove n $ garden // [((yMin, xMax), Plot {reachable = True})],
length $ getReachableAfterNMove n $ garden // [((yMax, xMin), Plot {reachable = True})],
length $ getReachableAfterNMove n $ garden // [((yMax, xMax), Plot {reachable = True})]]
getReachableAfterN :: Int -> Garden -> Int
getReachableAfterN n garden =
let ((yMin, xMin), (yMax, xMax)) = bounds garden
x = div (n - div (yMax - yMin) 2) (yMax - yMin + 1)
in x * x * getReachableEven garden + x * sum (getReachableEvenCorners garden)
+ (x - 1) * (x - 1) * getReachableOdd garden + (x - 1) * sum (getReachableOddCorners garden)
+ sum (getReachableCardinals garden)