Data commit

Task/Five-weekends/GAP/five-weekends.gap

@@ -0,0 +1,33 @@
+# return a list of two lists :
+# first is the list of months with five weekends between years y1 and y2 (included)
+# second is the list of years without such months, in the same interval
+FiveWeekends := function(y1, y2)
+  local L, yL, badL, d, m, y;
+  L := [ ];
+  badL := [ ];
+  for y in [y1 .. y2] do
+    yL := [ ];
+    for m in [1, 3, 5, 7, 8, 10, 12] do
+      if WeekDay([1, m, y]) = "Fri" then
+        d := StringDate([1, m, y]);
+        Add(yL, d{[4 .. 11]});
+      fi;
+    od;
+    if Length(yL) = 0 then
+      Add(badL, y);
+    else
+      Append(L, yL);
+    fi;
+  od;
+  return [ L, badL ];
+end;
+
+r := FiveWeekends(1900, 2100);;
+n := Length(r[1]);
+# 201
+Length(r[2]);
+# 29
+r[1]{[1 .. 5]};
+# [ "Mar-1901", "Aug-1902", "May-1903", "Jan-1904", "Jul-1904" ]
+r[1]{[n-4 .. n]};
+# [ "Mar-2097", "Aug-2098", "May-2099", "Jan-2100", "Oct-2100" ]