Source code in the icon programming language

procedure main(A)
every write(lastsundays(!A))
end
 
procedure lastsundays(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 = 6 do z -:=1 # backup to last sunday (6)
   suspend sprintf("%d-%d-%d",year,m,d+z)
   }
end
 
link datetime, printf