Zeller's Congruence Algorithm in Python | Find Day of a Date.

Zeller's Congruence is an algorithm devised by Christian Zeller to calculate the day of the week for a given date. It's a simple algorithm that works for any date in the Gregorian calendar. The formula is as follows:

Where:

• h is the day of the week (0 = Saturday, 1 = Sunday, ..., 6 = Friday)
• q is the day of the month
• m is the month (3 = March, 4 = April, ..., 14 = February; January and February are counted as months 13 and 14 of the previous year)
• K is the year of the century (i.e., year mod 100)
• J is the zero-based century (actually ⌊ year/100 ⌋)

Python Program to Find the Day of a Date.

We use Zeller's Congruence Algorithm to find the day of any date in Python. Below is the code implementation to do so.

Python Code.

# Python code to find day of week for any date
def zellers_congruence(day, month, year):
    if month < 3:
        month += 12
        year -= 1

    K = year % 100
    J = year // 100

    h = (day + (13 * (month + 1)) // 5 + K + K // 4 + J // 4 - 2 * J) % 7

    # List of day names
    days_of_week = ["Saturday", "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]

    # Adjust result (0 corresponds to Saturday)
    return days_of_week[(h + 5) % 7]

# Example
day = 25
month = 7
year = 2023
day_of_week = zellers_congruence(day, month, year)
print(f"The day of the week for {day}-{month}-{year} is {day_of_week}.")

Output:

The day of the week for 25-7-2023 is Sunday.

This code takes a date as input and returns the day of the week using Zeller's Congruence. The result is an integer where 0 corresponds to Saturday, 1 to Sunday, and so on. We are using a list of days to replace the output integer with matching day of the week.