Is Day of the Week easy or hard?

Day of the Week is categorized as an Easy problem on LeetCode with an acceptance rate around 59%. The logic becomes straightforward when using built-in libraries, while implementing the mathematical formula adds a moderate conceptual challenge.

Day of the Week Python/Java solution

In Python, you can use the built-in datetime module and call weekday() or strftime to get the weekday name. In Java, LocalDate from java.time provides getDayOfWeek(). Both implementations compute the result in constant time.

How to solve Day of the Week in O(1)?

Use a direct calendar formula such as Zeller's Congruence. The formula converts the given day, month, and year into a weekday index using integer division and modular arithmetic. After computing the result modulo 7, map the number to the correct weekday string.

What is the best approach for Day of the Week?

The most practical approach uses built-in date libraries available in languages like Python, Java, and JavaScript. These libraries already implement optimized calendar algorithms and return the weekday in O(1) time. For interviews, implementing Zeller's Congruence is often preferred because it demonstrates understanding of calendar math and modular arithmetic.

Is Day of the Week asked at Google/Amazon/Meta?

Calendar and date calculation problems appear occasionally in interviews because they test attention to detail and mathematical reasoning. Variations of weekday calculation or date arithmetic have appeared in interviews at companies like Google and Amazon.

What data structure is used in Day of the Week?

No complex data structure is required. The solution relies mainly on arithmetic operations and a small array or list to map weekday indices (0–6) to names such as Sunday, Monday, and Tuesday.

What is the time complexity of Day of the Week?

Both common solutions run in O(1) time and O(1) space because the calculation involves only a fixed number of arithmetic operations or a single library call. No iteration or additional data structures are required.

Description Hints 3 Solution Video 13:00

1185. Day of the Week

Easy59.6% acceptance3 companies

Given a date, return the corresponding day of the week for that date.

The input is given as three integers representing the day, month and year respectively.

Return the answer as one of the following values {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}.

Example 1:

Input: day = 31, month = 8, year = 2019
Output: "Saturday"

Example 2:

Input: day = 18, month = 7, year = 1999
Output: "Sunday"

Example 3:

Input: day = 15, month = 8, year = 1993
Output: "Sunday"

Constraints:

The given dates are valid dates between the years 1971 and 2100.

Asked at 3 companies

Zoho

Google Microsoft

Topics

Math

Hints open one at a time

Hint 1

Sum up the number of days for the years before the given year.

Hint 2

Handle the case of a leap year.

Hint 3

Find the number of days for each month of the given year.

13:00

Still stuck?Read 3 approaches, or watch a walkthrough.

Open solution

LanguageLoading editor…

1class Solution:
2    def dayOfTheWeek(self, day: int, month: int, year: int) -> str:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2Case 3

Input

31
8
2019

Input

18
7
1999

Input

15
8
1993

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