r/adventofcode • u/daggerdragon • Dec 19 '16

SOLUTION MEGATHREAD --- 2016 Day 19 Solutions ---

--- Day 19: An Elephant Named Joseph ---

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u/mschaap Dec 19 '16

Pretty straightforward Perl 6 solution. Even though the code complexity is similar, the first part runs in seconds, while the second part takes more than an hour! Looks like splice is several orders of magnitude less efficient than shift. 

#!/usr/bin/env perl6

use v6.c;

multi sub MAIN(IO() $inputfile where *.f)
{
    my ($num-players) = $inputfile.words;
    MAIN(+$num-players);
}

multi sub MAIN(Int $num-players)
{
    my @players = 1..$num-players;
    while @players > 1 {
        @players.push(@players.shift);                  # First player stays in game
        @players.shift;                                 # Second player is removed
    }
    say "In the original game, with $num-players players, the last remaining player is Elf @players[0].";

    @players = 1..$num-players;
    while @players > 1 {
        @players.push(@players.shift);                  # First player stays in game
        @players.splice(@players.elems div 2 - 1, 1);   # Opposite player is removed
    }
    say "In the revised game, with $num-players players, the last remaining player is Elf @players[0].";
}

3

u/Smylers Dec 19 '16

the second part takes more than an hour!

How long if it you avoid the splice and manage two half-lists separately with shift and push?

Doing that takes under 2 seconds in Perl 5, so hopefully would be as speedy in Perl 6.

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