AOC 2020 09

var input = File.ReadAllLines("input.txt");
var data = input.Select(l => long.Parse(l)).ToArray();

var preamble = new Queue<long>(data.Take(25).ToArray());
bool find(long num) {
    foreach (var i in preamble) {
        if (i > num) continue;
        foreach (var j in data) {
            if (j > num) continue;
            if (i + j == num) return true;
        }
    }
    return false;
}
(bool ok, long number) part1() {
    foreach (var i in data.Skip(25)) {
        if (i < preamble.Min() || i > preamble.Max() * 2 || !find(i)) {
            return (true, i);
        }
        preamble.Enqueue(i);
        preamble.Dequeue();
    }
    return (false, 0);
}

var p1 = part1();
Console.WriteLine($"Part 1: {p1}");

long part2() {
    for (int i = 0; i < data.Length; ++i) {
        var sum = data[i];
        for (int j = i + 1; j < data.Length; j++) {
            sum += data[j];
            if (sum == p1.number) {
                return data[i..j].Min() + data[i..j].Max();
            }
        }
    }
    return -1;
}
var p2 = part2();
Console.WriteLine($"Part 2: {p2}");