advent-of-code/2021/nim/day6.nim
2021-12-13 09:53:03 -06:00

46 lines
1.5 KiB
Nim

import std/[strutils, sequtils, tables, strformat]
import ./common
const DEFAULT_DAYS = 80
const CYCLE_DAYS = 7
const MATURING_DAYS = 2
proc lanternFish(input: string, days = DEFAULT_DAYS): int =
# a place to put newly-spawned fish that are not mature enough themselves to
# spawn within the cycle
var maturingFish: seq[(int, int)]
# here we will keep the counts of fish that spawn on a given day in the cycle
var fish = newSeq[int](CYCLE_DAYS)
# initialize our current fish counts based on the input
for i in input.split(',').mapIt(it.parseInt()): inc fish[i]
for day in 0..days:
let cycleDay = day mod CYCLE_DAYS
# since we're just about to decrement the days for all maturing fish, add
# 1 to offset and spawn our maturing fish
maturingFish.add((MATURING_DAYS+1, fish[cycleDay]))
# age maturing fish
for v in maturingFish.mitems(): dec v[0]
# if our oldest maturing fish have now matured move them to their place in
# the cycle
if maturingFish[0][0] == 0:
fish[cycleDay] += maturingFish[0][1]
maturingFish.delete(0)
# sum all fish counts plus the fish that were spawned two days ago
fish.foldl(a + b) + (if maturingFish[0][0] <= 1: maturingFish[0][1] else: 0)
let input = 6.loadInputText()
time("day 6 part 1"): echo input.lanternFish()
time("day 6 part 2"): echo input.lanternFish(256)
when not defined(release):
let testInput = "3,4,3,1,2"
doAssert testInput.lanternFish(18) == 26
doAssert testInput.lanternFish() == 5934
doAssert testInput.lanternFish(256) == 26984457539