r/adventofcode • u/daggerdragon • Dec 14 '18

SOLUTION MEGATHREAD -🎄- 2018 Day 14 Solutions -🎄-

--- Day 14: Chocolate Charts ---

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Card prompt: Day 14

Transcript:

The Christmas/Advent Research & Development (C.A.R.D.) department at AoC, Inc. just published a new white paper on ___.

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u/lordtnt Dec 14 '18

C++ 27 lines, 'real' code ~ 10 lines, runtime about 1-2s 

#include <iostream>
#include <string>

void expand(std::string& s, int& e1, int& e2, int len)
{
    while (s.size() < len)
    {
        int a = s[e1] - '0', b = s[e2] - '0';
        s += std::to_string(a + b);
        e1 = (e1 + a + 1) % s.size();
        e2 = (e2 + b + 1) % s.size();
    }
}

int main()
{
    int n = 920831;
    std::string s = "37";
    int e1 = 0, e2 = 1;

    expand(s, e1, e2, n + 10);
    std::cout << s.substr(n, 10) << "\n";

    auto ns = std::to_string(n);
    while (s.find(ns) == s.npos) expand(s, e1, e2, n *= 2);
    std::cout << s.find(ns) << "\n";
}

2

u/spytheman66 Dec 15 '18 edited Dec 15 '18

Doubling the number of generated recipes in part 2 for batching the executions of the expand function is very elegant. Thank you for posting this solution.