passdoors.c

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv) {
  int number_of_doors = atoi(argv[1]);
  int number_of_passes = atoi(argv[2]);
  int open_doors = 0;

  for (int i = 1; i <= number_of_doors; i++) {
    int toggles = 0;
    for (int j = 1; j <= number_of_passes; j++) {
      toggles += i % j == 0 ? 1 : 0;
    }
    open_doors += toggles % 2;
  }

  printf("%d\n", open_doors);
}

passdoors.py

import sys


def odd_number_of_divisors(n, number_of_passes):
    """Counts the number of times the door is toggled, and returns True if left open after a number of passes."""
    return sum((n % i == 0 for i in range(1, number_of_passes + 1))) % 2 == 1


def pass_doors(number_of_doors, number_of_passes):
    if number_of_passes > number_of_doors:
        number_of_passes = number_of_doors
    return sum(
        (
            odd_number_of_divisors(i, number_of_passes)
            for i in range(1, number_of_doors + 1)
        )
    )


if __name__ == "__main__":
    print(pass_doors(int(sys.argv[1]), int(sys.argv[2])))

passdoors.zig

const std = @import("std");

pub fn count_open_doors(number_of_doors: usize, number_of_passes: usize) usize {
    var open_doors: usize = 0;
    var i: usize = 1;
    while (i <= number_of_doors) : (i += 1) {
        var j: usize = 1;
        var toggles: usize = 0;
        while (j <= number_of_passes) : (j += 1) {
            toggles += @boolToInt(i % j == 0);
        }
        open_doors += toggles % 2;
    }
    return open_doors;
}

pub fn main() !void {
    const allocator = std.heap.page_allocator;
    const args = try std.process.argsAlloc(allocator);
    defer std.process.argsFree(allocator, args);

    if (args.len < 3) return error.ExpectedArgument;

    const number_of_doors: usize = try std.fmt.parseInt(usize, args[1], 10);
    const number_of_passes: usize = try std.fmt.parseInt(usize, args[2], 10);
    const open_doors: usize = count_open_doors(number_of_doors, number_of_passes);

    const stdout = std.io.getStdOut().writer();
    try stdout.print("{}\n", .{open_doors});
}