def find(lines, index, search)
    if index > (lines.first.length() - 2)
        raise "Invalid index"
    end

    bits = [0, 0]

    # Count the occurrences of each digit at the index
    lines.each do |line|
        digit = Integer(line[index])
        bits[digit] += 1
    end

    # Not the most expressive way to do this, but should get the job done
    if search == 1
        # Return most common value, or 1 on a tie
        target = bits[0] > bits[1] ? 0 : 1
    else
        # Return least common value, or 0 on a tie
        target = bits[0] <= bits[1] ? 0 : 1
    end

    # Filter lines to only the ones that have the target value at `index`
    lines = lines.filter { |line| line[index] == target.to_s }

    # If there's only one left, we found our value.
    # Otherwise, continue filtering at the next index
    if lines.length() == 1
        return lines.first
    else
        return find(lines, index + 1, search)
    end
end

def run(f)
    lines = f.readlines()
    # This should filter down to a single number, which we need to convert from a base 2 bit string
    oxygen = find(lines, 0, 1).to_i(2)
    co2 = find(lines, 0, 0).to_i(2)

    return oxygen * co2
end