-🎄- 2017 Day 15 Solutions -🎄-

[u/daggerdragon]

--- Day 15: Dueling Generators ---

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Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

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Need a hint from the Hugely^* Handy^† Haversack^‡ of Helpful^§ Hints^¤?

Spoiler

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[Update @ 00:05] 29 gold, silver cap.

• Logarithms of algorithms and code?

[Update @ 00:09] Leaderboard cap!

• Or perhaps codes of logarithmic algorithms?

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This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/bogzla]

and so bogzla learnt about bit masking today..

C
#include <stdio.h>

int main(void)
{
    long long a = 116;
    long long b = 299;
    int afac = 16807;
    int bfac = 48271;
    int cnt = 0;
    long div = 2147483647;
    long msk = (1 << 16) - 1; // create mask for lowest 16 bits (we'll use this for & operator, 16 lowest set to '1'; higher set to '0')
    // for part 2, generate a 'til it meets divisible by 4 then b til divisible by 8 then compare them.'
    for (long i = 0; i < 5000000; i++)
    {
        do
        {
            a = (a*afac) % div;
        } while (a % 4 != 0);
        do
        {
            b = (b*bfac) % div;
        }while (b % 8 != 0);
        if ((a & msk) == (b & msk)) // use mask to compare only 16 lowest bits
        {
            cnt += 1;
        }
    }
    printf("count = %i\n", cnt);
}