Python | Print number of leap years from given list of years

The problem of finding leap year is quite generic and we might face the issue of finding the number of leap years in given list of years. Let’s discuss certain ways in which this can be performed.

Method #1: Using Iteration
Check whether year is a multiple of 4 and not multiple of 100 or year is multiple of 400. 

Python3

# Python code to finding number of
# leap years in list of years.

# Input list initialization
Input = [2001, 2002, 2003, 2004, 2005, 2006,
         2007, 2008, 2009, 2010, 2011, 2012]

# Find whether it is leap year or not
def checkYear(year):
    return (((year % 4 == 0) and
             (year % 100 != 0)) or
             (year % 400 == 0))

# Answer Initialization
Answer = 0

for elem in Input:
    if checkYear(elem):
        Answer = Answer + 1

# Printing
print("No of leap years are:", Answer)

Output:

No of leap years are: 3

Time Complexity: O(n) where n is the size of the list.

Auxiliary Space: O(1)

Method #2: Using calendar

Python3

# Python code to finding number of
# leap years in list of years.

# Importing calendar
import calendar

# Input list initialization
Input = [2001, 2002, 2003, 2004, 2005,
         2006, 2007, 2008, 2009, 2010]

# Using calendar to find leap year
def FindLeapYear(Input):
    ans = 0
    for elem in Input:
        if calendar.isleap(int(elem)):
            ans = ans + 1
    return ans

Output = FindLeapYear(Input)

# Printing
print("No of leap years are:", Output)

Output:

No of leap years are: 2

Time Complexity: O(n) where n is the size of the list.

Auxiliary Space: O(1)

Method #3:Using a list comprehension

This method involves using a list comprehension to create a list of all the leap years in the input list, and then finding the length of that list. Here’s an example of how it could be done:

Python3

# Input list initialization
Input = [2001, 2002, 2003, 2004, 2005, 2006,
         2007, 2008, 2009, 2010, 2011, 2012]

# Find leap years
leap_years = [year for year in Input if year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)]

# Find number of leap years
Answer = len(leap_years)

print("No of leap years are:", Answer)
#This code is contributed by Edula Vinay Kumar Reddy

Output

No of leap years are: 3

Time Complexity: O(n) where n is the size of the list.

Auxiliary Space: O(1)