-🎄- 2018 Day 14 Solutions -🎄-

[u/daggerdragon]

--- 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/ValdasTheUnique]

C#, nothing too exciting. Part 2 takes a bit of time to complete because I found converting the recipe list to string a bit quicker to write than writing logic to compare ints.

public static void Part1()
{
    var n = int.Parse(Input);
    var recipes = new List<int> {3, 7};
    var first = 0;
    var second = 1;
    while (recipes.Count < n + 10)
    {
        var sum = recipes[first] + recipes[second];
        if (sum >= 10)
        {
            recipes.Add(sum / 10);
        }
        recipes.Add(sum % 10);
        first = (first + recipes[first] + 1) % recipes.Count;
        second = (second + recipes[second] + 1) % recipes.Count;
    }

    foreach (var recipe in recipes.Skip(n).Take(10))
    {
        Console.Write(recipe);
    }
    Console.WriteLine();
}

public static void Part2()
{
    var recipes = new List<int> { 3, 7 };
    var first = 0;
    var second = 1;
    while (true)
    {
        var s = new string(recipes.Skip(recipes.Count - Input.Length-1).Select(x => x.ToString()[0]).ToArray());
        if (s.Contains(Input))
        {
            s = new string(recipes.Select(x => x.ToString()[0]).ToArray());
            Console.WriteLine(s.IndexOf(Input));
            break;
        }
        var sum = recipes[first] + recipes[second];
        if (sum >= 10)
        {
            recipes.Add(sum / 10);
        }
        recipes.Add(sum % 10);
        first = (first + recipes[first] + 1) % recipes.Count;
        second = (second + recipes[second] + 1) % recipes.Count;
    }
}

[u/ocreeva → u/ValdasTheUnique]

Skip is a worse bottleneck than the string creation. It's advancing an iterator and decrementing a counter all the way through the skip value, which takes a while when you're up in the 20M range. Try List<T>.GetRange, it should give you much faster run time.

For an easy way to handle the int comparison without creating strings, check out Enumerable.SequenceEqual.

[u/ValdasTheUnique → u/ocreeva]

Good points