1154. Day of the Year

Description

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

Example 1:

• Input: date = “2019-01-09”
• Output: 9
• Explanation: Given date is the 9th day of the year in 2019.

Example 2:

• Input: date = “2019-02-10”
• Output: 41

Constraints:

• date.length == 10
• date[4] == date[7] == '-', and all other date[i]’s are digits
• date represents a calendar date between Jan 1^st, 1900 and Dec 31^st, 2019.

💡 Hint 1:
Have a integer array of how many days there are per month. February gets one extra day if its a leap year. Then, we can manually count the ordinal as day + (number of days in months before this one).

Submitted Code

class Solution:
    def dayOfYear(self, date: str) -> int:
        year, month, day = map(int, date.split("-"))
        
        feb_days = 29 if year % 400 == 0 or (year % 4 == 0 and year % 100 != 0) else 28
        month_days = [31, feb_days, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
        
        return sum(month_days[:month-1]) + day

Runtime: 13 ms | Beats 42.16%
Memory: 17.13 MB | Beats 99.72%

그레고리력 윤년 계산 규칙

1. 연도가 4의 배수이면 윤년 후보이다.
2. 윤년 후보 중 100의 배수는 제외된다.
3. 100의 배수더라도 400의 배수이면 윤년이다.

Other Solutions

1st

class Solution:
    def dayOfYear(self, date: str) -> int:
        # we first make a list of days in a year when a specific
        # month ends
        list_year=[0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334]

        day=int(date[-2:])
        year=int(date[:4])
        month=int(date[5:7])

        # if year is leap and february is gone, add an extra day 
        if year%4==0 and year!=1900 and month>2 :
            day+=1

        #return days of specific month + date
        return list_year[month-1]+day

time complexity: 𝑂(1)
space complexity: 𝑂(1)

월별 누적 일수를 미리 적어놓는 방법도 있다.

2nd

class Solution:
    def ordinalOfDate(self, date):
        Y, M, D = map(int, date.split('-'))
        return int((datetime.datetime(Y, M, D) - datetime.datetime(Y, 1, 1)).days + 1)

문자열을 datetime 타입으로 변경하면 월별 일수를 몰라도 자동으로 계산할 수 있다.