Doomsday rule: Difference between revisions

=={{header|J}}==

To find the doomsday for a month, find the number of days for each month in that year, and compute the running sum from right to left. Then add 1 to each of those numbers, find the mod 7 remainder and add 1 again

<lang J> 1+7|1++/\.31 28 31 30 31 30 31 31 30 31 30 31

3 7 7 4 2 6 4 1 5 3 7 5

1+7|1++/\.31 29 31 30 31 30 31 31 30 31 30 31

4 1 7 4 2 6 4 1 5 3 7 5</lang>

Also note that adding 7 is like adding 0 in modulo 7 arithmetic.

Thus:

<lang J>get_weekday=: {{ 'Y M D'=. y

Y0=. todayno Y,1 1

Y1=. todayno 1+Y,0 0

aday=. M{1+7|1++/\.0,>.//./}.|:todate Y0+i.Y1-Y0

dday=. 7|2 5 4 6+/ .*1,4 100 400|/Y

'day',~;(7|D+dday-aday){;:'Sun Mon Tues Wednes Thurs Fri Satur'

}}</lang>

Task examples:

<lang J> get_weekday 1800 1 6

Monday

get_weekday 1875 3 29

Monday

get_weekday 1915 12 7

Tuesday

get_weekday 1970 12 23

Wednesday

get_weekday 2043 5 14

Thursday

get_weekday 2077 2 12

Friday

get_weekday 2101 4 2

Saturday</lang>