Last Friday of each month
Write a program or a script that returns the last Fridays of each month of a given year provided as argument on the command line.
Example of an expected output:
./last_fridays 2012 2012-01-27 2012-02-24 2012-03-30 2012-04-27 2012-05-25 2012-06-29 2012-07-27 2012-08-31 2012-09-28 2012-10-26 2012-11-30 2012-12-28
- Cf.
C
Doesn't work with Julian calendar (then again, you probably don't need to plan your weekends for middle ages).
<lang c>#define _XOPEN_SOURCE
- include <stdio.h>
- include <stdlib.h>
int main(int c, char *v[]) { int days[] = {31,29,31,30,31,30,31,31,30,31,30,31}; int m, y, w;
if (c < 2 || (y = atoi(v[1])) <= 1700) return 1;
days[1] -= (y % 4) || (!(y % 100) && (y % 400));
w = y * 365 + (y - 1) / 4 - (y - 1) / 100 + (y - 1) / 400 + 6;
for(m = 0; m < 12; m++) { w = (w + days[m]) % 7; printf("%d-%02d-%d\n", y, m + 1, days[m] + (w < 5 ? -2 : 5) - w); }
return 0; }</lang>
C++
called with ./last_fridays 2012
<lang cpp>#include <boost/date_time/gregorian/gregorian.hpp>
- include <iostream>
- include <cstdlib>
int main( int argc , char* argv[ ] ) {
using namespace boost::gregorian ;
greg_month months[ ] = { Jan , Feb , Mar , Apr , May , Jun , Jul ,
Aug , Sep , Oct , Nov , Dec } ;
greg_year gy = atoi( argv[ 1 ] ) ;
for ( int i = 0 ; i < 12 ; i++ ) {
last_day_of_the_week_in_month lwdm ( Friday , months[ i ] ) ;
date d = lwdm.get_date( gy ) ;
std::cout << d << std::endl ;
}
return 0 ;
}</lang> Output:
2012-Jan-27 2012-Feb-24 2012-Mar-30 2012-Apr-27 2012-May-25 2012-Jun-29 2012-Jul-27 2012-Aug-31 2012-Sep-28 2012-Oct-26 2012-Nov-30 2012-Dec-28
Icon and Unicon
This will write the last fridays for every year given as an argument. There is no error checking on the year.
<lang Icon>procedure main(A) every write(lastfridays(!A)) end
procedure lastfridays(year) every m := 1 to 12 do {
d := case m of {
2 : if IsLeapYear(year) then 29 else 28
4|6|9|11 : 30
default : 31
} # last day of month
z := 0
j := julian(m,d,year) + 1 # first day of next month
until (j-:=1)%7 = 4 do z -:=1 # backup to last friday=4
suspend sprintf("%d-%d-%d",year,m,d+z)
}
end
link datetime, printf</lang>
printf.icn provides formatting datetime.icn provides julian and IsLeapYear
Output:
last_fridays.exe 2012 2012-1-27 2012-2-24 2012-3-30 2012-4-27 2012-5-25 2012-6-29 2012-7-27 2012-8-31 2012-9-28 2012-10-26 2012-11-30 2012-12-28
J
<lang j>require'dates' last_fridays=: 12 {. [:({:/.~ }:"1)@(#~ 5 = weekday)@todate (i.366) + todayno@,&1 1</lang>
In other words, start from January 1 of the given year, and count forward for 366 days, keeping the fridays. Then pick the last friday within each represented month. Then pick the first 12 (since on a non-leap year which ends on a thursday we would get an extra friday).
Example use:
<lang j> last_fridays 2012 2012 1 27 2012 2 24 2012 3 30 2012 4 27 2012 5 25 2012 6 29 2012 7 27 2012 8 31 2012 9 28 2012 10 26 2012 11 30 2012 12 28</lang>
Java
<lang java5>import java.text.DateFormatSymbols; import java.util.Calendar; import java.util.GregorianCalendar;
public class LastFriday {
private static int[] months = {Calendar.JANUARY, Calendar.FEBRUARY,
Calendar.MARCH, Calendar.APRIL, Calendar.MAY, Calendar.JUNE,
Calendar.JULY, Calendar.AUGUST, Calendar.SEPTEMBER, Calendar.OCTOBER,
Calendar.NOVEMBER, Calendar.DECEMBER};
public static void main(String[] args){
int year = Integer.parseInt(args[0]);
boolean leapYear = new GregorianCalendar().isLeapYear(year);
for(int month:months){
int days = 31;
switch(month){
case Calendar.SEPTEMBER:
case Calendar.APRIL:
case Calendar.JUNE:
case Calendar.NOVEMBER:
days = 30;
break;
case Calendar.FEBRUARY:
days = leapYear ? 29 : 28;
default:
}
GregorianCalendar date = new GregorianCalendar(year, month, days);
while(date.get(Calendar.DAY_OF_WEEK) != Calendar.FRIDAY){
date.add(Calendar.DAY_OF_MONTH, -1);
}
String monthStr = new DateFormatSymbols().getShortMonths()[month];
System.out.println(monthStr +" "+ date.get(Calendar.DAY_OF_MONTH));
}
}
}</lang>
Output (for java LastFriday 2012):
Jan 27 Feb 24 Mar 30 Apr 27 May 25 Jun 29 Jul 27 Aug 31 Sep 28 Oct 26 Nov 30 Dec 28
OCaml
Using the module Unix from the standard OCaml library:
<lang ocaml>#load "unix.cma" open Unix
let usage() =
Printf.eprintf "%s <year>\n" Sys.argv.(0); exit 1
let print_date t =
Printf.printf "%d-%02d-%02d\n" (t.tm_year + 1900) (t.tm_mon + 1) t.tm_mday
let is_date_ok tm t =
(tm.tm_year = t.tm_year && tm.tm_mon = t.tm_mon && tm.tm_mday = t.tm_mday)
let () =
let _year =
try int_of_string Sys.argv.(1)
with _ -> usage()
in
let year = _year - 1900 in
let fridays = Array.make 12 (Unix.gmtime 0.0) in
for month = 0 to 11 do
for day_of_month = 1 to 31 do
let tm = { (Unix.gmtime 0.0) with
tm_year = year;
tm_mon = month;
tm_mday = day_of_month;
} in
let _, t = Unix.mktime tm in
if is_date_ok tm t (* check for months that have less than 31 days *)
&& t.tm_wday = 5 (* is a friday *)
then fridays.(month) <- t
done;
done;
Array.iter print_date fridays</lang>
Output:
$ ocaml last_fridays.ml 2012 2012-01-27 2012-02-24 2012-03-30 2012-04-27 2012-05-25 2012-06-29 2012-07-27 2012-08-31 2012-09-28 2012-10-26 2012-11-30 2012-12-28
With a dedicated library
<lang ocaml>open CalendarLib
let usage() =
Printf.eprintf "%s <year>\n" Sys.argv.(0); exit 1
let print_date (year, month, day) =
Printf.printf "%d-%02d-%02d\n" year month day
let () =
let year =
try int_of_string Sys.argv.(1)
with _ -> usage()
in
let fridays = ref [] in
for month = 1 to 12 do
let num_days = Date.days_in_month (Date.make_year_month year month) in
let rec aux day =
if Date.day_of_week (Date.make year month day) = Date.Fri
then fridays := (year, month, day) :: !fridays
else aux (pred day)
in
aux num_days
done;
List.iter print_date (List.rev !fridays)</lang>
Run this script with the command:
ocaml unix.cma str.cma -I +calendar calendarLib.cma last_fridays.ml 2012
Perl
<lang Perl>#!/usr/bin/perl -w use strict ; use DateTime ; use feature qw( say ) ;
foreach my $month ( 1..12 ) {
my $dt = DateTime->last_day_of_month( year => $ARGV[ 0 ] , month => $month ) ;
while ( $dt->day_of_week != 5 ) {
$dt->subtract( days => 1 ) ;
}
say $dt->ymd ;
}</lang> Output:
2012-01-27 2012-02-24 2012-03-30 2012-04-27 2012-05-25 2012-06-29 2012-07-27 2012-08-31 2012-09-28 2012-10-26 2012-11-30 2012-12-28
Pike
<lang Pike>int(0..1) last_friday(object day) {
return day->week_day() == 5 &&
day->month_day() > day->month()->number_of_days()-7;
}
int main(int argc, array argv) {
array days = filter(Calendar.Year((int)argv[1])->months()->days()[*], last_friday);
write("%{%s\n%}", days->format_ymd());
return 0;
}</lang>
Ruby
<lang ruby>require 'date'
def last_friday(year, month)
if month == 12 d = Date.new(year+1, 1, 1) else d = Date.new(year, month+1, 1) end begin d -= 1 end until d.wday == 5 # Ruby 1.9: d.friday? d
end
year = Integer(ARGV.shift) (1..12).each {|month| puts last_friday(year, month)}</lang>
Using the ActiveSupport library for some convenience methods
<lang ruby>require 'rubygems' require 'activesupport'
def last_friday(year, month)
d = Date.new(year, month, 1).end_of_month until d.wday == 5 d = d.yesterday end d
end</lang>
Tcl
<lang tcl>package require Tcl 8.5 set year [lindex $argv 0] foreach dm {02/1 03/1 04/1 05/1 06/1 07/1 08/1 09/1 10/1 11/1 12/1 12/32} {
# The [clock scan] code is unhealthily clever; use it for our own evil purposes set t [clock scan "last friday" -base [clock scan $dm/$year -gmt 1] -gmt 1] # Print the interesting part puts [clock format $t -format "%Y-%m-%d" -gmt 1]
}</lang> Sample execution:
$ tclsh8.5 lastfri.tcl 2012 2012-01-27 2012-02-24 2012-03-30 2012-04-27 2012-05-25 2012-06-29 2012-07-27 2012-08-31 2012-09-28 2012-10-26 2012-11-30 2012-12-28
UNIX Shell
Using ncal. Will switch to Julian calender as ncal sees fit, and will not calculate past year 9999 (chances are you'll be too dead by then to worry about weekends anyway).
<lang bash>#!/bin/sh
if [ -z $1 ]; then exit 1; fi
- weed out multiple erros due to bad year
ncal 1 $1 > /dev/null && \ for m in 01 02 03 04 05 06 07 08 09 10 11 12; do echo $1-$m-`ncal $m $1 | grep Fr | sed 's/.* \([0-9]\)/\1/'` done</lang>
Using date --date from GNU date??? This code is not portable.
<lang bash>#!/bin/sh
- Free code, no limit work
- $Id: lastfridays,v 1.1 2011/11/10 00:48:16 gilles Exp gilles $
- usage :
- lastfridays 2012 # prints last fridays of months of year 2012
debug=${debug:-false}
- debug=true
epoch_year_day() { #set -x x_epoch=`expr ${2:-0} '*' 86400 + 43200` date --date="${1:-1970}-01-01 UTC $x_epoch seconds" +%s }
year_of_epoch() { date --date="1970-01-01 UTC ${1:-0} seconds" +%Y } day_of_epoch() { LC_ALL=C date --date="1970-01-01 UTC ${1:-0} seconds" +%A } date_of_epoch() { date --date="1970-01-01 UTC ${1:-0} seconds" "+%Y-%m-%d" } month_of_epoch() { date --date="1970-01-01 UTC ${1:-0} seconds" "+%m" }
last_fridays() { year=${1:-2012}
next_year=`expr $year + 1`
$debug && echo "next_year $next_year"
current_year=$year
day=0
previous_month=01
while test $current_year != $next_year; do
$debug && echo "day $day"
current_epoch=`epoch_year_day $year $day`
$debug && echo "current_epoch $current_epoch"
current_year=`year_of_epoch $current_epoch`
current_day=`day_of_epoch $current_epoch`
$debug && echo "current_day $current_day"
test $current_day = 'Friday' && current_friday=`date_of_epoch $current_epoch`
$debug && echo "current_friday $current_friday"
current_month=`month_of_epoch $current_epoch`
$debug && echo "current_month $current_month"
# Change of month => previous friday is the last of month
test "$previous_month" != "$current_month" \
&& echo $previous_friday
previous_month=$current_month
previous_friday=$current_friday
day=`expr $day + 1`
done
}
- main
last_fridays ${1:-2012}</lang>
Sample execution:
lastfridays 2012 2012-01-27 2012-02-24 2012-03-30 2012-04-27 2012-05-25 2012-06-29 2012-07-27 2012-08-31 2012-09-28 2012-10-26 2012-11-30 2012-12-28