Write a Python program to find the day of the week for any particular date in the past or future. Let the input be in the format “dd mm yyyy”.
Examples:
Input : 03 02 1997 Output : Monday Input : 31 01 2019 Output : Thursday
The already discussed approach to find the day of the week for a given date is the Naive approach. Now, let’s discuss the pythonic approaches.
Approach #1 : Using weekday() provided by datetime module.
The weekday() function of date class in datetime module, returns an integer corresponding to the day of the week.
Python3
# Python program to Find day of# the week for a given dateimport datetimeimport calendardef findDay(date): born = datetime.datetime.strptime(date, '%d %m %Y').weekday() return (calendar.day_name[born])# Driver programdate = '03 02 2019'print(findDay(date)) |
Sunday
Approach #2 : Using strftime() method
The strftime() method takes one or more format codes as an argument and returns a formatted string based on it. Here we will pass the directive “%A” in the method which provides Full weekday name for the given date.
Python3
# Python program to Find day of# the week for a given dateimport datetimefrom datetime import dateimport calendardef findDay(date): day, month, year = (int(i) for i in date.split(' ')) born = datetime.date(year, month, day) return born.strftime("%A")# Driver programdate = '03 02 2019'print(findDay(date)) |
Sunday
Approach #3 : By finding day number
In this approach, we find the day number using calendar module and then find the corresponding week day.
Python3
# Python program to Find day of# the week for a given dateimport calendardef findDay(date): day, month, year = (int(i) for i in date.split(' ')) dayNumber = calendar.weekday(year, month, day) days =["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"] return (days[dayNumber])# Driver programdate = '03 02 2019'print(findDay(date)) |
Sunday
Time Complexity: O(1)
Auxiliary Space: O(1)
Approach#4: Using Zeller’s congruence
Algorithm
1. Use the strptime() method of the datetime module to convert the given input string into a datetime object.
2. Extract the day, month, and year from the datetime object.
3. Use Zeller’s congruence formula to calculate the day of the week.
4. Map the result from step 3 to the corresponding day of the week.
Python3
from datetime import datetimedef day_of_week(date_str): date_obj = datetime.strptime(date_str, '%d %m %Y') day = date_obj.day month = date_obj.month year = date_obj.year if month < 3: month += 12 year -= 1 century = year // 100 year_of_century = year % 100 day_num = (day + ((13 * (month + 1)) // 5) + year_of_century + (year_of_century // 4) + (century // 4) - (2 * century)) % 7-1 day_names = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'] return day_names[day_num]date_str = '03 02 2019'print(day_of_week(date_str)) |
Sunday
Time Complexity: O(1) – constant time is required to convert the input string into a datetime object and calculate the day of the week.
Space Complexity: O(1) – constant space is used.
