Code Golf: Calculate Orthodox Easter date

StackOverflow https://stackoverflow.com/questions/3584307

Question

The Challenge

Calculate the Date of the Greek Orthodox Easter (http://www.timeanddate.com/holidays/us/orthodox-easter-day) Sunday in a given Year (1900-2100) using the least amount of characters.

Input is just a year in the form '2010'. It's not relevant where you get it (Input, CommandLineArgs etc.) but it must be dynamic!

Output should be in the form day-month-year (say dd/mm/yyyy or d/m/yyyy)

Restrictions No standard functions, such as Mathematica's EasterSundayGreekOrthodox or PHP's easter_date(), which return the (not applicable gregorian) date automatic must be used!

Examples

2005 returns 1/5/2005
2006 returns 23/4/2006
2007 returns 8/4/2007
2008 returns 27/4/2008
2009 returns 19/4/2009
2010 returns 4/4/2010
2011 returns 24/4/2011
2012 returns 15/4/2012
2013 returns 5/5/2013
2014 returns 20/4/2014
2015 returns 12/4/2015

Code count includes input/output (i.e full program).

Edit: I mean the Eastern Easter Date.

Reference: http://en.wikipedia.org/wiki/Computus

Was it helpful?

Solution

Python (101 140 132 115 chars)

y=input()
d=(y%19*19+15)%30
e=(y%4*2+y%7*4-d+34)%7+d+127
m=e/31
a=e%31+1+(m>4)
if a>30:a,m=1,5
print a,'/',m,'/',y

This one uses the Meeus Julian algorithm but since this one only works between 1900 and 2099, an implementation using Anonymous Gregorian algorithm is coming right up.

Edit: Now 2005 is properly handled. Thanks to Mark for pointing it out.

Edit 2: Better handling of some years, thanks for all the input!

Edit 3: Should work for all years in range. (Sorry for hijacking it Juan.)

OTHER TIPS

PHP CLI, no easter_date(), 125 characters

Valid for dates from 13 March 1900 to 13 March 2100, now works for Easters that fall in May

Code:

<?=date("d/m/Y",mktime(0,0,0,floor(($b=($a=(19*(($y=$argv[1])%19)+15)%30)+(2*($y%4)+4*$y%7-$a+34)%7+114)/31),($b%31)+14,$y));

Invocation:

$ php codegolf.php 2010
$ php codegolf.php 2005

Output:

04/04/2010
01/05/2005

With whitespace:

<?=date("d/m/Y", mktime(0, 0, 0, floor(($b = ($a = (19 * (($y = $argv[1]) % 19) + 15) % 30) + (2 * ($y % 4) + 4 * $y % 7 - $a + 34) % 7 + 114) / 31), ($b % 31) + 14, $y));

This iteration is no longer readable thanks to PHP's handling of assignments. It's almost a functional language!

For completeness, here's the previous, 127 character solution that does not rely on short tags:

Code:

echo date("d/m/Y",mktime(0,0,0,floor(($b=($a=(19*(($y=$argv[1])%19)+15)%30)+(2*($y%4)+4*$y%7-$a+34)%7+114)/31),($b%31)+14,$y));

Invocation:

$ php -r 'echo date("d/m/Y",mktime(0,0,0,floor(($b=($a=(19*(($y=$argv[1])%19)+15)%30)+(2*($y%4)+4*$y%7-$a+34)%7+114)/31),($b%31)+14,$y));' 2010
$ php -r 'echo date("d/m/Y",mktime(0,0,0,floor(($b=($a=(19*(($y=$argv[1])%19)+15)%30)+(2*($y%4)+4*$y%7-$a+34)%7+114)/31),($b%31)+14,$y));' 2005

C#, 155 157 182 209 212 characters

class P{static void Main(string[]i){int y=int.Parse(i[0]),c=(y%19*19+15)%30,d=c+(y%4*2+y%7*4-c+34)%7+128;System.Console.Write(d%31+d/155+"/"+d/31+"/"+y);}}

Python 2.3, 97 characters

y=int(input())
c=(y%19*19+15)%30
d=c+(y%4*2+y%7*4-c+34)%7+128
print"%d/%d/%d"%(d%31+d/155,d/31,y)

This also uses the Meeus Julian algorithm (and should work for dates in May).

  • removed no longer necessary check for modern years and zero-padding in output
  • don't expect Easters in March anymore because there are none between 1800-2100
  • included Python 2.3 version (shortest so far)

Mathematica 

<<Calendar`;a=Print[#3,"/",#2,"/",#]&@@EasterSundayGreekOrthodox@#&

Invoke with 

a[2010]

Output

4/4/2010

Me too: I don't see the point in not using built-in functions.

Java - 252 196 190 chars

  • Update 1: The first algo was for Western Gregorian Easter. Fixed to Eastern Julian Easter now. Saved 56 chars :)

  • Update 2: Zero padding seem to not be required. Saved 4 chars.

class E{public static void main(String[]a){long y=new Long(a[0]),b=(y%19*19+15)%30,c=b+(y%4*2+y%7*4-b+34)%7+(y>1899&y<2100?128:115),m=c/31;System.out.printf("%d/%d/%d",c%31+(m<5?0:1),m,y);}}

With newlines

class E{
 public static void main(String[]a){
  long y=new Long(a[0]),
  b=(y%19*19+15)%30,
  c=b+(y%4*2+y%7*4-b+34)%7+(y>1899&y<2100?128:115),
  m=c/31;
  System.out.printf("%d/%d/%d",c%31+(m<5?0:1),m,y);
 }
}

JavaScript (196 characters)

Using the Meeus Julian algorithm. This implementation assumes that a valid four-digit year was given.

y=~~prompt();d=(19*(y%19)+15)%30;x=d+(2*(y%4)+4*(y%7)-d+34)%7+114;m=~~(x/31);d=x%31+1;if(y>1899&&y<2100){d+=13;if(m==3&&d>31){d-=31;m++}if(m==4&&d>30){d-=30;m++}}alert((d<10?"0"+d:d)+"/0"+m+"/"+y)

Delphi 377 335 317 characters

Single line:

var y,c,n,i,j,m:integer;begin Val(ParamStr(1),y,n);c:=y div 100;n:=y-19*(y div 19);i:=c-c div 4-(c-((c-17)div 25))div 3+19*n+15;i:=i-30*(i div 30);i:=i-(i div 28 )*(1-(i div 28)*(29 div(i+1))*((21 -n)div 11));j:=y+y div 4 +i+2-c+c div 4;j:=j-7*(j div 7);m:=3+(i-j+40 )div 44;Write(i-j+28-31*(m div 4),'/',m,'/',y)end.

Formatted:

var
  y,c,n,i,j,m:integer;
begin
  Val(ParamStr(1),y,n);
  c:=y div 100;
  n:=y-19*(y div 19);
  i:=c-c div 4-(c-((c-17)div 25))div 3+19*n+15;
  i:=i-30*(i div 30);
  i:=i-(i div 28 )*(1-(i div 28)*(29 div(i+1))*((21 -n)div 11));
  j:=y+y div 4 +i+2-c+c div 4;j:=j-7*(j div 7);
  m:=3+(i-j+40 )div 44; 
  Write(i-j+28-31*(m div 4),'/',m,'/',y)
end.

Tcl

Eastern Easter

(116 chars)

puts [expr 1+[incr d [expr ([set y $argv]%4*2+$y%7*4-[
set d [expr ($y%19*19+15)%30]]+34)%7+123]]%30]/[expr $d/30]/$y

Uses the Meeus algorithm. Takes the year as a command line argument, produces Eastern easter. Could be a one-liner, but it's slightly more readable when split...

Western Easter

(220 chars before splitting over lines)

interp alias {} tcl::mathfunc::s {} set;puts [expr [incr 3 [expr {
s(2,(s(4,$argv)%100/4*2-s(3,(19*s(0,$4%19)+s(1,$4/100)-$1/4-($1-($1+8)/25+46)
/3)%30)+$1%4*2-$4%4+4)%7)-($0+11*$3+22*$2)/451*7+114}]]%31+1]/[expr $3/31]/$4

Uses the Anonymous algorithm.

COBOL, 1262 chars

WORKING-STORAGE SECTION.

01 V-YEAR       PIC S9(04) VALUE 2010.
01 V-DAY        PIC S9(02) VALUE ZERO.
01 V-EASTERDAY  PIC S9(04) VALUE ZERO.
01 V-CENTURY    PIC S9(02) VALUE ZERO.
01 V-GOLDEN     PIC S9(04) VALUE ZERO.
01 V-GREGORIAN  PIC S9(04) VALUE ZERO.
01 V-CLAVIAN    PIC S9(04) VALUE ZERO.
01 V-FACTOR     PIC S9(06) VALUE ZERO.
01 V-EPACT      PIC S9(06) VALUE ZERO.

PROCEDURE DIVISION

XX-CALCULATE EASTERDAY.

   COMPUTE V-CENTURY = (V-YEAR / 100) + 1
   COMPUTE V-GOLDEN= FUNCTION MOD(V-YEAR, 19) + 1
   COMPUTE V-GREGORIAN = (V-CENTURY * 3) / 4 - 12
   COMPUTE V-CLAVIAN
        = (V-CENTURY * 8 + 5) / 25 - 5 - V-GREGORIAN
   COMPUTE V-FACTOR
        = (V-YEAR * 5) / 4 - V-GREGORIAN - 10
   COMPUTE V-EPACT
   = FUNCTION MOD((V-GOLDEN * 11 + 20 + V-CLAVIAN), 30)

   IF V-EPACT = 24
      ADD 1 TO V-EPACT
   ELSE
      IF V-EPACT = 25
         IF V-GOLDEN > 11
            ADD 1 TO V-EPACT
         END-IF
      END-IF
   END-IF

  COMPUTE V-DAY = 44 - V-EPACT

  IF V-DAY < 21
     ADD 30 TO V-DAY
  END-IF

  COMPUTE V-DAY
  = V-DAY + 7 - (FUNCTION MOD((V-DAY + V-FACTOR), 7))

  IF V-DAY <= 31
     ADD 300 TO V-DAY GIVING V-EASTERDAY
  ELSE
     SUBTRACT 31 FROM V-DAY
     ADD 400 TO V-DAY GIVING V-EASTERDAY
  END-IF
  .
XX-EXIT.
   EXIT.

Note: Not mine, but I like it

EDIT: I added a char count with spaces but I don't know how spacing works in COBOL so I didn't change anything from original. ~vlad003

UPDATE: I've found where the OP got this code: http://www.tek-tips.com/viewthread.cfm?qid=31746&page=112. I'm just putting this here because the author deserves it. ~vlad003

C, 128 121 98 characters

Back to Meeus' algorithm. Computing the day in Julian, but adjusting for Gregorian (this still seems naive to me, but I cannot find a shorter alternative).

main(y,v){int d=(y%19*19+15)%30;d+=(y%4*2+y%7*4-d+34)%7+128;printf("%d/%d/%d",d%31+d/155,d/31,y);}

I have not found a case where floor(d/31) would actually be needed. Also, to account for dates in May, the m in Meeus' algorithm must be at least 5, therefore the DoM is greater than 154, hence the division.

The year is supplied as the number of program invocation arguments plus one, ie. for 1996 you must provide 1995 arguments. The range of ARG_MAX on modern systems is more than enough for this.

PS. I see Gabe has come to the same implementation in Python 2.3, surpassing me by one character. Aw. :( PPS. Anybody looking at a tabular method for 1800-2099?

Edit - Shortened Gabe's answer to 88 characters:

y=input()
d=(y%19*19+15)%30
d+=(y%4*2+y%7*4-d+34)%7+128
print"%d/%d/%d"%(d%31+d/155,d/31,y)

BASIC, 973 chars

Sub EasterDate (d, m, y)

   Dim FirstDig, Remain19, temp    'intermediate results
   Dim tA, tB, tC, tD, tE          'table A to E results

   FirstDig = y \ 100              'first 2 digits of year
   Remain19 = y Mod 19             'remainder of year / 19

' calculate PFM date
   temp = (FirstDig - 15) \ 2 + 202 - 11 * Remain19

   Select Case FirstDig
      Case 21, 24, 25, 27 To 32, 34, 35, 38
         temp = temp - 1
      Case 33, 36, 37, 39, 40
         temp = temp - 2
   End Select
   temp = temp Mod 30

   tA = temp + 21
   If temp = 29 Then tA = tA - 1
   If (temp = 28 And Remain19 > 10) Then tA = tA - 1

'find the next Sunday
   tB = (tA - 19) Mod 7

   tC = (40 - FirstDig) Mod 4
   If tC = 3 Then tC = tC + 1
   If tC > 1 Then tC = tC + 1

   temp = y Mod 100
   tD = (temp + temp \ 4) Mod 7

   tE = ((20 - tB - tC - tD) Mod 7) + 1
   d = tA + tE

'return the date
   If d > 31 Then
      d = d - 31
      m = 4
   Else
      m = 3
   End If

End Sub

Credit: Astronomical Society of South Australia

EDIT: I added a char count but I think many spaces could be removed; I don't know BASIC so I didn't make any changes to the code. ~vlad003

I'm not going to implement it, but I'd like to see one where the code e-mails the Pope, scans any answer that comes back for a date, and returns that.

Admittedly, the calling process may be blocked for a while.

Javascript 125 characters

This will handle years 1900 - 2199. Some of the other implementations cannot handle the year 2100 correctly.

y=prompt();k=(y%19*19+15)%30;e=(y%4*2+y%7*4-k+34)%7+k+127;m=~~(e/31);d=e%31+m-4+(y>2099);alert((d+=d<30||++m-34)+"/"+m+"/"+y)

Ungolfed..ish

// get the year to check.
y=prompt();

// do something crazy.
k=(y%19*19+15)%30;

// do some more crazy...
e=(y%4*2+y%7*4-k+34)%7+k+127;

// estimate the month. p.s. The "~~" is like Math.floor
m=~~(e/31);

// e % 31 => get the day
d=e%31;
if(m>4){
    d += 1;
}
if(y > 2099){
   d += 1;
}

// if d is less than 30 days add 1
if(d<30){
   d += 1;
}
// otherwise, change month to May
// and adjusts the days to match up with May.
// e.g., 32nd of April is 2nd of May
else{
    m += 1;
    d = m - 34 + d;
}

// alert the result!
alert(d + "/" + m + "/" + y);

A fix for dates up to 2399.
I'm sure there is a way to algorithmically calculate dates beyond this but I don't want to figure it out.

y=prompt();k=(y%19*19+15)%30;e=(y%4*2+y%7*4-k+34)%7+k+127;m=~~(e/31);d=e%31+m-4+(y<2200?0:~~((y-2000)/100));alert((d+=d<30||++m-34)+"/"+m+"/"+y)

'VB .Net implementation of:
'http://aa.usno.navy.mil/faq/docs/easter.php
Dim y As Integer = 2010
Dim c, d, i, j, k, l, m, n As Integer
c = y \ 100
n = y - 19 * (y \ 19)
k = (c - 17) \ 25
i = c - c \ 4 - (c - k) \ 3 + 19 * n + 15
i = i - 30 * (i \ 30)
i = i - (i \ 28) * (1 - (i \ 28) * (29 \ (i + 1)) * ((21 - n) \ 11))
j = y + y \ 4 + i + 2 - c + c \ 4
j = j - 7 * (j \ 7)
l = i - j
m = 3 + (l + 40) \ 44
d = l + 28 - 31 * (m \ 4)
Easter = DateSerial(y, m, d)
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