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|
module Day09
open System.IO
open Common
let directionToVec =
function
| 'U' -> Vec2.up
| 'R' -> Vec2.right
| 'D' -> Vec2.down
| 'L' -> Vec2.left
| char -> failwithf "Invalid direction: %c" char
let parseHeadMoves =
Seq.collect (fun (line: string) -> Seq.replicate (int line[2..]) (directionToVec line[0]))
let moveTail head tail =
if Vec2.chebyshevDist head tail <= 1 then
tail
else
tail + Vec2.sign (head - tail)
let createRope length = List.replicate length Vec2.zero
let solution ropeLength =
parseHeadMoves
>> Seq.scan
(fun rope headMove ->
match rope with
| head :: tail -> List.scan moveTail (head + headMove) tail
| [] -> [])
(createRope ropeLength)
>> Seq.map Seq.last
>> Util.countDistinct
let test = File.ReadLines("test.txt")
assert (solution 2 test = 13)
assert (solution 10 test = 1)
let input = File.ReadLines("input.txt")
printfn "%d" <| solution 2 input
printfn "%d" <| solution 10 input
|
