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Day of the Year

Difficulty: Easy

Problem Description

Given a string date representing a Gregorian calendar date formatted as YYYY-MM-DD, return the day number of the year.

Key Insights

  • The problem requires calculating the day of the year based on a given date.
  • The Gregorian calendar has different days in February depending on whether it's a leap year.
  • The problem can be solved by summing the days of the months leading up to the given date.

Space and Time Complexity

Time Complexity: O(1)
Space Complexity: O(1)

Solution

To solve the problem, we will:

  1. Extract the year, month, and day from the input date string.
  2. Create an array that stores the number of days in each month for a non-leap year.
  3. Check if the year is a leap year and adjust the days in February accordingly.
  4. Sum the days of the months preceding the given month and add the current day to get the day number of the year.

Code Solutions

def dayOfYear(date: str) -> int:
    year = int(date[:4])
    month = int(date[5:7])
    day = int(date[8:10])
    
    # Days in each month for a non-leap year
    days_in_month = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
    
    # Check for leap year
    if (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0):
        days_in_month[1] = 29  # February has 29 days in a leap year
    
    # Calculate the day of the year
    return sum(days_in_month[:month - 1]) + day
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