(1) To judge whether a year is a leap year, you only need to look at the last two digits of the year. If the last two digits are divisible by 4, it is a leap year, otherwise it is not.

(2) When the last two digits are all 0, we will look at the first two digits of the year; If the first two digits are divisible by 4, it is a leap year, and vice versa.

(3) If the two digits at the end of 2004 are 04, it can be directly regarded as 1 bit. If this number is divisible by 4, it is a leap year, otherwise it is not.