The submarine has been making some odd creaking noises, so you ask it to produce a diagnostic report just in case.

The diagnostic report (your puzzle input) consists of a list of binary numbers which, when decoded properly, can tell you many useful things about the conditions of the submarine. The first parameter to check is the power consumption.

Read the full puzzle.

using System;
using System.Linq;

namespace AdventOfCode.Y2021.Day03;

[ProblemName("Binary Diagnostic")]
class Solution : Solver {

    public object PartOne(string input) {
        var diagnosticReport = input.Split("\n");
        return GammaRate(diagnosticReport) * EpsilonRate(diagnosticReport);
    }

    public object PartTwo(string input) {
        var diagnosticReport = input.Split("\n");
        return OxygenGeneratorRating(diagnosticReport) * Co2ScruberRating(diagnosticReport);
    }

    int GammaRate(string[] diagnosticReport) => Extract1(diagnosticReport, MostCommonBitAt);
    int EpsilonRate(string[] diagnosticReport) => Extract1(diagnosticReport, LeastCommonBitAt);
    int OxygenGeneratorRating(string[] diagnosticReport) => Extract2(diagnosticReport, MostCommonBitAt);
    int Co2ScruberRating(string[] diagnosticReport) => Extract2(diagnosticReport, LeastCommonBitAt);

    char MostCommonBitAt(string[] lines, int ibit) =>
        2 * lines.Count(line => line[ibit] == '1') >= lines.Length ? '1' : '0';

    char LeastCommonBitAt(string[] lines, int ibit) =>
        MostCommonBitAt(lines, ibit) == '1' ? '0' : '1';

    int Extract1(string[] lines, Func<string[], int, char> selectBitAt) {
        var cbit = lines[0].Length;

        var bits = "";
        for (var ibit = 0; ibit < cbit; ibit++) {
            bits += selectBitAt(lines, ibit);
        }
        return Convert.ToInt32(bits, 2);
    }

    int Extract2(string[] lines, Func<string[], int, char> selectBitAt) {
        var cbit = lines[0].Length;

        for (var ibit = 0; lines.Length > 1 && ibit < cbit; ibit++) {
            var bit = selectBitAt(lines, ibit);
            lines = lines.Where(line => line[ibit] == bit).ToArray();
        }

        return Convert.ToInt32(lines[0], 2);
    }
}

Please ☆ my repo if you like it!