var lines = File.ReadAllLines("/Users/alr1wn0/Projects/code1/input.txt")

    .ToList();

​

var count = lines.Count;

var length = lines[0].Length;

​

int oxygen = GetOxygen(lines);

int co2 = GetCO2(lines);

​

Console.WriteLine(oxygen * co2);

​

Console.ReadLine();

​

int GetOxygen(List<string> lines)

{

    var length = lines[0].Length;

​

    int result = 0;

​

    for (int i = 0; i < 12; i++)

    {

        lines = FilterLinesOxygen(lines, i);

        if (lines.Count == 1)

        {

            result = Convert.ToInt32(lines[0], 2);

            break;

        }

    }

​

    return result;

}

​

List<string> FilterLinesOxygen(List<string> lines, int index)

{

    var linesA = lines.Where(x => x[index] == '0').ToList();

    var linesB = lines.Where(x => x[index] == '1').ToList();

​

    if (linesA.Count > linesB.Count)

        return linesA;

    else if (linesA.Count < linesB.Count)

        return linesB;

    else

        return linesB;

}

​

int GetCO2(List<string> lines)

{

    var length = lines[0].Length;

​

    int result = 0;

​

    for (int i = 0; i < 12; i++)

    {

        lines = FilterLinesCO2(lines, i);

        if (lines.Count == 1)

        {

            result = Convert.ToInt32(lines[0], 2);

            break;

        }

    }

​

    return result;

}

​

List<string> FilterLinesCO2(List<string> lines, int index)

{

    var linesA = lines.Where(x => x[index] == '0').ToList();

    var linesB = lines.Where(x => x[index] == '1').ToList();

​

    if (linesA.Count > linesB.Count)

        return linesB;

    else if (linesA.Count < linesB.Count)

        return linesA;

    else

        return linesA;

}