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Thursday Code Puzzler: How Many Weekends?

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Thursday is code puzzler day here at DZone. The idea is simple: solve the coding problem as efficiently as you can, in any language or framework that you find suitable.

Note: Even though there really is nothing stopping you from finding a solution to this on the internet, try to keep honest, and come up with your own answer.  It's all about the participation!

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How Many Weekends?

Write a function that takes two dates and returns the number of weekends between those dates. If either of the start or end dates is a weekend, you can count that. And whether it's a Saturday or Sunday (doesn't need to include both), it counts.

Catch up on all our previous puzzlers here.


Neeraj Khapre replied on Thu, 2012/09/13 - 4:49am

public class WeekendCalculater {

	public static void main(String[] args) throws ParseException {
		SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");

		Calendar startDate = Calendar.getInstance();

		Calendar endDate = Calendar.getInstance();

		System.out.println("Total no. of Weekends are : "
				+ calculateWeekends(startDate, endDate));

	public static int calculateWeekends(Calendar startDate, Calendar endDate) {
		// Return 0 if startDate and endDate are same
		if (startDate.equals(endDate)) {
			return 0;

		int weekend_count = 0;
		int count = 0;

		while (startDate.compareTo(endDate) == -1) {
			startDate.add(Calendar.DAY_OF_MONTH, 1);

			if (startDate.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY
					|| startDate.get(Calendar.DAY_OF_WEEK) == Calendar.SATURDAY) {
				if (count == 2) {
					count = 0;
		return weekend_count;

Leandro Santos replied on Thu, 2012/09/13 - 10:32am

Here is the code in ruby:


class WeekendsCalculator
  attr_reader :days
  def initialize(start_at,end_at)
    @days = parse_range(start_at,end_at)
  def parse_range(start_at, end_at)
    if start_at.is_a?(String) && end_at.is_a?(String)
    elsif start_at.is_a?(Date) && end_at.is_a?(Date)
      raise "Start_at and end_at should be either strings or date objects"
  def weekends
    days.inject(0) do |weekends,day|
      weekends += 1 if day.saturday?
c = WeekendsCalculator.new('2012-08-01', '2012-09-07')
puts "The number of weekends is #{c.weekends}"

Vijay Nathani replied on Thu, 2012/09/13 - 9:49pm

Groovy solution using open source library jodaTime.

import org.joda.time.*;
class ComputeWeekends {
	private def st, en;
	private int pre;
	private boolean isWeekend(date) { [DateTimeConstants.SATURDAY, DateTimeConstants.SUNDAY].contains(date.dayOfWeek().get())}
	private def gotoMiddleOfWeek(startOrEnd) {
		boolean lastDateWeekend = false
		while (st <= en ) {
			def d = startOrEnd?st:en
		    if (d.dayOfWeek().get() == DateTimeConstants.WEDNESDAY) return
			pre += (isWeekend(d) && !lastDateWeekend)?1:0
			lastDateWeekend = isWeekend(d)
	def weekendsBetween(start,end) {
		if (start > end) return 0
		(st, en, pre) = [ start, end, 0]
		Days.daysBetween(st,en).days / DateTimeConstants.DAYS_PER_WEEK + pre 
println new ComputeWeekends().weekendsBetween(new DateMidnight(2012, 9, 4), new DateMidnight(2012, 9, 22)) //prints 3

ebenezer raj replied on Thu, 2012/09/13 - 2:04pm

In q { x:x[0]+til 1+x[1]-x[0]; x:x-`week$x; x[where x within (5 6)]:-1; x:?[(prev x)=-1;0;x]; count x[where x=-1] }[(2012.09.01;2012.09.13)] prints out 2

Joe Colburn replied on Thu, 2012/09/13 - 6:43pm

function weekends($date1, $date2) {
    $epoch1 = strtotime($date1);
    $epoch2 = strtotime($date2);
    $weekends = floor((($epoch2 - $epoch1) / 86400) / 7);
    if (substr(date("D", $epoch1), 0, 1) == "S") {
    if (substr(date("D", $epoch2), 0, 1) == "S") {

    return $weekends;

Vijay Nathani replied on Thu, 2012/09/13 - 9:51pm in response to: Joe Colburn

Will this code work for boundary conditions e.g. weekends between 8 and 9-Sep-2012?

Joe Colburn replied on Thu, 2012/09/13 - 11:47pm in response to: Vijay Nathani

Good question... If you mean when the first date is Sep 8 2012 and the second is Sep 9 2012, I believe it will fail, counting it as 2 weekends, but that should be the only failing scenario.  Good catch!

Vijay Nathani replied on Fri, 2012/09/14 - 12:10am in response to: Joe Colburn

Even when both start and end dates are the same weekend date e.g. 8-Sep-2012 , the code will fail.

If start date is after end date, then too the code fails.

If start date is 9-Sep-12 and end date is 16-Sep-12, then too the code fails.

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