Given day number, convert to date it refers to.
Input : day_num = “339”, year = “2020”
Output : 12-04-2020
Explanation : 339th Day of 2020 is 4th December.Input : day_num = “4”, year = “2020”
Output : 01-04-2020
Explanation : 4th Day of 2020 is 4th January.
Method #1 : Using datetime.strptime()
In this, we get the year string and day number string, and pass to strptime(), converts to the corresponding required date.
Python3
# Python3 code to demonstrate working of# Convert day number to date in particular year# Using datetime.strptime()from datetime import datetime# initializing day numberday_num = "339"# print day numberprint("The day number : " + str(day_num))# adjusting day numday_num.rjust(3 + len(day_num), '0')# Initialize yearyear = "2020"# converting to dateres = datetime.strptime(year + "-" + day_num, "%Y-%j").strftime("%m-%d-%Y")# printing resultprint("Resolved date : " + str(res)) |
The day number : 339 Resolved date : 12-04-2020
Method #2 : Using timedelta()
In this, we initialize the date by 1st of January and then add number of days using timedelta(), resultant gives the date required.
Python3
# Python3 code to demonstrate working of# Convert day number to date in particular year# Using datetime.strptime()from datetime import datetime, date, timedelta# initializing day numberday_num = "339"# print day numberprint("The day number : " + str(day_num))# adjusting day numday_num.rjust(3 + len(day_num), '0')# Initialize yearyear = "2020"# Initializing start datestrt_date = date(int(year), 1, 1)# converting to dateres_date = strt_date + timedelta(days=int(day_num) - 1)res = res_date.strftime("%m-%d-%Y")# printing resultprint("Resolved date : " + str(res)) |
The day number : 339 Resolved date : 12-04-2020
Time Complexity: is O(1), as it involves basic arithmetic operations, datetime operations, and string operations that take constant time.
Auxiliary Space: is O(1), as it uses only a fixed number of variables and does not require any data structure to store data.
Method #3: Using divmod()
This program converts a day number and year into a date using the datetime module in Python. It adjusts the day number and initializes a start date, and then adds the number of days to the start date using timedelta(). Finally, it formats the resulting date string using strftime() and prints the result.
Python3
# Python3 code to demonstrate working of# Convert day number to date in particular year# Using datetime.strptime()from datetime import datetime, date, timedelta# initializing day numberday_num = "339"# print day numberprint("The day number : " + str(day_num))# adjusting day numday_num = day_num.rjust(3 + len(day_num), '0')# Initialize yearyear = "2020"# Initializing start datestrt_date = date(int(year), 1, 1)# converting to dateres_date = strt_date + timedelta(days=int(day_num) - 1)res = res_date.strftime("%m-%d-%Y")# printing resultprint("Resolved date : " + str(res)) |
The day number : 339 Resolved date : 12-04-2020
Time complexity: O(1) as it does not depend on the size of the input.
Auxiliary space: O(1) as it only uses a fixed number of variables to store the input and output, and does not depend on the size of the input.
Method 4 : date.fromordinal() method.
This method takes a proleptic Gregorian ordinal and returns the corresponding date.
Here’s the step-by-step approach:
- Initialize the day number and the year.
- Convert the year to a proleptic Gregorian ordinal using the date.toordinal() method.
- Add the day number to the ordinal obtained in step 2 and subtract 1 to get the proleptic Gregorian ordinal of the desired date.
- Convert the proleptic Gregorian ordinal to a date using the date.fromordinal() method.
- Format the date as required.
Python3
# Python3 code to demonstrate working of# Convert day number to date in particular year# Using date.fromordinal()from datetime import date# initializing day numberday_num = "339"# print day numberprint("The day number : " + str(day_num))# adjusting day numday_num = day_num.rjust(3 + len(day_num), '0')# Initialize yearyear = "2020"# Convert year to a proleptic Gregorian ordinalyear_ordinal = date(int(year), 1, 1).toordinal()# Calculate proleptic Gregorian ordinal of the desired datedesired_ordinal = year_ordinal + int(day_num) - 1# Convert proleptic Gregorian ordinal to dateres_date = date.fromordinal(desired_ordinal)# Format the dateres = res_date.strftime("%m-%d-%Y")# printing resultprint("Resolved date : " + str(res)) |
The day number : 339 Resolved date : 12-04-2020
The time complexity of this approach is O(1) .
The Auxiliary space required is O(1) as well.
Method #5: Using dateutil.parser.parse() method
Step-by-step approach:
- Import the required module dateutil:
- Initialize the year and day number:
- Create a string representing the date using the format YYYY-DDD, where YYYY is the year and DDD is the day number:
- Use the parse() method to parse the string and convert it to a datetime object:
- Convert the datetime object to a date object:
- Format the result using the strftime() method:
- Print the result:
Python3
from datetime import timedeltafrom dateutil import parser# initializing year and day numberyear = "2020"day_num = "339"# creating date stringdate_str = year + "-01-01" # January 1st of the given yeardate_obj = parser.parse(date_str) # parse date string to datetime object# adding days to datetime objectdate_res = date_obj + timedelta(days=int(day_num) - 1)# formatting result dateres = date_res.strftime("%m-%d-%Y")# printing resultprint("Resolved date : " + str(res)) |
OUTPUT: Resolved date : 12-04-2020
Time complexity: The time complexity of this method is O(1) as it does not involve any loops or iterations.
Auxiliary space: The auxiliary space used by this method is O(1) as it does not require any additional data structures.
