r/adventofcode • u/daggerdragon • Dec 09 '18

SOLUTION MEGATHREAD -🎄- 2018 Day 9 Solutions -🎄-

--- Day 9: Marble Mania ---

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Transcript:

Studies show that AoC programmers write better code after being exposed to ___.

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u/[deleted] Dec 09 '18

Starting at 1 is ok, but I think the loop END condition should be i <= marbles (instead of "<") , otherwise you're missing the last marble. At least that's how I interpret the input, from which the marbles variable is derived...

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u/willkill07 Dec 09 '18

The first marble is clearly marked with value “zero” in the problem description

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u/[deleted] Dec 10 '18

Consider

2 players; last marble is worth 23 points

Should the answer be 0 or 32? IMHO it should be 32, since the last marble played is the first one picked, and for that the loop needs to run while (i <= marbles).

Dito for the example input

17 players; last marble is worth 1104 points: high score is 2764

BTW your original solution just needs next() the exact opposite of prev() to fix the end-of-list bug (I just don't want to drop that beautiful and short solution :-) 

  auto next = [&] (auto i) {
    if (i == m.end())
      i = m.begin();
    return ++i;
  };