Python Program to Print the Incremented Date if valid

In this article, we will write a python program to input a date and check whether it is a valid date or not. If it is valid, output the incremented date. Otherwise, print “Invalid date”.

Examples:

Input : 1/2/2000
Output: 2/2/2000

Input : 29/2/2002
Output: Invalid date

Input : 31/12/2015
Output: 1/1/2016 

The first step is to check whether the entered date is valid or not. For this step, we need to first obtain the maximum possible day number for the month entered. Then we need to see whether the day lies between 1 and the obtained maximum day number and whether the month lies between 1 and 12. If both these conditions get satisfied, that means it is a valid date, and we need to increment it. To increment the date, we need to handle the following cases:

1. If the entered date is the last day of the year.
2. If the entered date is the last day of the month.
3. If the entered date is not the last day of the month.

For the first case, increment the year and set both the day and the month to 1.  For the second case, increment the month and set the day to 1. For the third case, just increment the day. If even one of the two conditions did not get satisfied, then it is an invalid date. 

Below is the implementation.

# input the date and split it to day, month and year
day, month, year = map(int, input().split('/'))

if month == 2:

    # check for February
    if year % 4 != 0:
        d_max = 28
    else:
        d_max = 29
        
elif month in [4, 6, 9, 11]:
  
    # check the months with 30 days
    d_max = 30

else:
    d_max = 31

if 1 <= day <= d_max and 1 <= month <= 12:
    
    # increment the date since it is a
    # valid date
    if day == d_max:
        day = 1
        if month == 12:
            
            # If this block is entered,
            # then it is the last day of
            # the year
            month = 1
            year += 1
        else:
          
            # If this block is entered, 
            # then it is the last day of 
            # the month
            month += 1
    else:
      
        # If this block is entered, then it
        # is NOT the last day of the month
        day += 1
    print(str(day) + "/" + str(month) + "/" + str(year))
else:
    print("Invalid date")

Output:

31/12/2015
1/1/2016

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