1. Ways of Thinking About Problems
Leap Year – After and including 1582, Evenly divisible by 4, except evenly divisible by 100,
except evenly divisible by 400.
Not leap year – Before 1582, Not evenly divisible by 4 and evenly
divisible by 100 and not 400.
All years
Pre 1582
Post 1582
NOT
% 4 == 0
% 100 == 0
% 400 == 0 IS
NOT

2. All years
Pre 1582
= and post 1582
NOT
% 4 == 0
% 100 == 0
% 400 == 0 IS
NOT
if (year < 1582)
“is not a leap year”
else if (year % 400 == 0)
“ is a leap year”
else if (year % 100 == 0)
“ is not a leap year”
else if (year % 4 == 0)
“ is a leap year
else

3. All years
Pre 1582
= and post 1582
NOT
% 4 == 0
% 100 == 0
% 400 == 0 IS
NOT
if (year < 1582)
“is not a leap year”
else if (year % 4 != 0)
else if (year % 400 == 0)
“ is a leap year”
else if (year % 100 == 0)
“ is not a leap year”
else
“ is a leap year “
This variant seeks to eliminate most of
the cases before we get down to the more
specific leap year candidate cases.

4. There are many other solutions