aoc_2020_day_15.nim

# Second edition of the solution using Table[int, int]. This is possible
# because we only care about a repetition of the last spoken number, I
# misunderstood an example as more generic than what it is, the rules of
# the game are clear about this.

import strutils, sequtils, tables

var input = "8,11,0,19,1,2".split(',').map(parseInt)

var turns: Table[int, int]
for i, n in input[0 .. ^2]:
  turns[n] = i + 1

var mostRecentlySpoken = input[^1]
for turn in input.len .. 2019:
  var next = 0
  if mostRecentlySpoken in turns:
    next = turn - turns[mostRecentlySpoken]
  turns[mostRecentlySpoken] = turn
  mostRecentlySpoken = next

echo mostRecentlySpoken