How do you solve Day of the Year on LeetCode?

Day of the Year (LeetCode #1154) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(1) time complexity and O(1) space complexity. Key insight: Understanding leap years is crucial for accurate date calculations.

What is the brute force solution for Day of the Year?

The brute force approach for Day of the Year is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute-force approach involves manually counting the days from the start of the year to the given date. This is straightforward but inefficient, as it requires checking each month and its days. The optimal Optimal Solution approach improves this to O(1).

What algorithm or data structure is used to solve Day of the Year?

Day of the Year uses the following concepts: Math, String. The recommended patterns to study are: Array, Mathematical calculations.

What are the interview tips for Day of the Year?

Always clarify the input format and constraints with the interviewer. Think aloud while coding to demonstrate your thought process. Consider edge cases, such as leap years and the first/last days of the year.

What are common mistakes when solving Day of the Year?

Failing to account for leap years correctly. Not parsing the date string accurately, leading to incorrect indices.

#1154

Day of the Year

Easy

MathStringArrayMathematical calculations

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(1)
Space	O(1)	O(1)

💡

Intuition

Time O(1)Space O(1)

The optimal approach efficiently calculates the day of the year by leveraging pre-defined arrays for month days and a simple leap year check, allowing us to compute the result in constant time.

⚙️

Algorithm

4 steps

1Step 1: Parse the input date string to extract the year, month, and day.
2Step 2: Create an array that holds the number of days in each month for a non-leap year.
3Step 3: Check if the year is a leap year and adjust February's days if necessary.
4Step 4: Use a single loop or direct indexing to sum the days of the months preceding the given month and add the day of the current month.

solution.py9 lines

1# Full working Python code
2
3def day_of_year(date: str) -> int:
4    year, month, day = map(int, date.split('-'))
5    days_in_month = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
6    if (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0):
7        days_in_month[1] = 29
8    return sum(days_in_month[:month-1]) + day
9

ℹ

Complexity note: The complexity is O(1) because the operations performed do not depend on the size of the input; they are constant-time operations based on fixed arrays.

1Understanding leap years is crucial for accurate date calculations.
2Using pre-defined arrays for month days allows for efficient summation.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.