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Given a date string in the form Day Month Year, where:

• Day is a numerical day followed by a suffix (st, nd, rd, th).
• Month is the full name of the month with the first letter in uppercase.
• Year is a four-digit number.

Your task is to reformat the date to the format YYYY-MM-DD, where:

• YYYY is the four-digit year.
• MM is the two-digit month.
• DD is the two-digit day.

Example

Input: "20th Oct 2052"
Output: "2052-10-20"

Input: "6th Jun 1933"
Output: "1933-06-06"

Input: "26th May 1960"
Output: "1960-05-26"

Clarifying Questions

1. Should input strings always be valid and follow the specified format?
   • Yes, assume input strings are always correctly formatted.
2. What is the range of years we could expect?
   • Any valid four-digit year (e.g., 1000 to 9999).

Strategy

1. Extract Components: Extract Day, Month, and Year from the input string.
2. Remove Suffix: Remove the suffix from the Day part.
3. Month Mapping: Create a mapping from month names to their corresponding two-digit numbers.
4. Format Components: Ensure that the Day and Month are two digits (prefix with 0 if necessary).
5. Concatenate Result: Combine Year, Month, and Day into the desired format.

Code

def reformat_date(date: str) -> str:
    # Split the input string into parts
    parts = date.split()
    
    # Extract day (and remove suffix), month, and year
    day = parts[0][:-2]
    month = parts[1]
    year = parts[2]
    
    # Map months to their corresponding two-digit numbers
    month_map = {
        "Jan": "01", "Feb": "02", "Mar": "03", "Apr": "04",
        "May": "05", "Jun": "06", "Jul": "07", "Aug": "08",
        "Sep": "09", "Oct": "10", "Nov": "11", "Dec": "12"
    }
    
    # Convert day to two digits
    if len(day) == 1:
        day = '0' + day
    
    # Format result
    formatted_date = f"{year}-{month_map[month]}-{day}"
    
    return formatted_date

# Examples
print(reformat_date("20th Oct 2052"))  # Output: "2052-10-20"
print(reformat_date("6th Jun 1933"))   # Output: "1933-06-06"
print(reformat_date("26th May 1960"))  # Output: "1960-05-26"

Time Complexity

The time complexity for this solution is O(1) because:

• String splitting and key lookups in a dictionary are O(1) operations.
• String manipulation operations (like slicing, concatenation) are O(1).

This ensures that our solution processes the input in constant time, independent of the length of the string or the specific content of the date.

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