License Key Formatting

Here’s the Python function for the problem statement. It reformats the given license key to have exactly k characters in each group, except for the first group, and ensures all lowercase letters are converted to uppercase.

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class Solution:
    def licenseKeyFormatting(self, s: str, k: int) -> str:
        # Removing all the dashes and converting the letters to uppercase
        s = s.replace("-", "").upper()

        # Finding the length of the license key without dashes
        length = len(s)

        # Finding the length of the first group
        first_group_length = length % k or k

        # Adding the first group to the result
        result = s[:first_group_length]

        # Iterating through the rest of the characters, grouping by k characters, and adding dashes
        for i in range(first_group_length, length, k):
            result += "-" + s[i:i + k]

        return result

Explanation

  1. We start by removing all dashes from the string and converting it to uppercase.
  2. We calculate the length of the first group using the modulus operator.
  3. We add the first group to the result, which can be shorter than k but must contain at least one character.
  4. We iterate through the rest of the characters, grouping them by k characters, and adding dashes between the groups.
  5. We return the final reformatted license key.

Identifying Problem Isomorphism

“License Key Formatting” is approximately isomorphic to “Reformat The String”.

Reasoning:

Both problems involve reformatting strings under certain rules. In “License Key Formatting”, you are required to reformat the given license key according to the rules. Similarly, in “Reformat The String”, you need to rearrange the string such that no two adjacent characters are the same type.

“Add Strings” is another similar problem.

Reasoning:

This problem requires you to perform addition on two non-negative integers given as string. The connection to the “License Key Formatting” problem lies in the manipulation of strings to obtain a desired output.

Based on simplicity, the order is:

  1. Reformat The String
  2. License Key Formatting
  3. Add Strings

“Reformat The String” is simpler as it only involves reordering the characters of a string. “License Key Formatting” is slightly more complex because it requires reordering and grouping of characters. “Add Strings” is the most complex because it involves not only string manipulation, but also mathematical operations.

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class Solution:
    def licenseKeyFormatting(self, S: str, K: int) -> str:
        S = S.replace('-', '')
        head = len(S) % K
        grouping = []

        if head:
            grouping.append( S[:head] )

        for index in range(head, len(S), K ):
            grouping.append( S[ index : index+K ] )

        return '-'.join( grouping ).upper()

Problem Classification

This problem falls under the category of “String Manipulation”. It involves the operations of reformatting and restructuring a string according to certain rules.

  • We have a license key represented as a string, s, which contains alphanumeric characters and dashes. This string is split into n+1 groups by n dashes.
  • We are also given an integer, k, which defines the required length of each group in the reformatted license key.
  • We need to reformat the string such that each group contains exactly k characters, except possibly for the first group which can be shorter than k but must contain at least one character.
  • We need to ensure that there is a dash between two groups and all lowercase letters are converted to uppercase.
  • The problem requires us to return the reformatted license key.

This can be further classified as a “Reformatting and Transformation” problem. It involves transforming the input string according to a set of given rules and returning the transformed string. The problem involves operations of string splitting, joining, transformation to uppercase, and restructuring.

Reformatting, in the context of data manipulation, refers to the process of changing the structure or presentation of data while keeping the underlying information the same.

In the context of the problem we’ve been discussing, reformatting is about changing how the license key string is presented. The characters and their order remain the same, but the structure in which they are grouped and presented is changed according to the rules specified.

Here is a simple example of reformatting:

Suppose you have a string of numbers “1234567890”, and you’re asked to reformat this string into a phone number format. In a common phone number format, the string could be reformatted as “(123) 456-7890”. Notice that the underlying sequence of numbers has not changed, but the presentation has been modified to fit the phone number format. That’s reformatting.

Transformation, in the context of data manipulation, refers to changing the data into a different format or type, which often involves changing the underlying information or representation of the data.

A simple example of transformation could be converting all the letters in a string from lowercase to uppercase. For instance, given a string “hello world”, transforming this string to uppercase would result in “HELLO WORLD”. Here, the underlying information in the string (the letters and their sequence) is being changed, as the lowercase letters have been transformed into their uppercase counterparts.

In the context of the problem statement you provided, transforming lowercase letters to uppercase is one of the tasks involved in solving the problem. This is a transformation operation because it changes the underlying representation of the characters in the string.

The difference is that reformatting does not change the value but transformation can change the value?

Yes, that’s a good way to understand the difference.

Reformatting often refers to changing the way information is presented or organized without altering the underlying information itself. A simple example could be changing the date format from “DD-MM-YYYY” to “YYYY/MM/DD”. The date itself remains the same; it’s just being presented differently.

On the other hand, transformation typically involves changing the actual data or the value. For instance, converting a string to uppercase changes the underlying data because “hello” and “HELLO” are not considered the same due to case sensitivity in many contexts.

In the context of this problem, reformatting refers to rearranging the license key to a certain pattern defined by ‘k’ characters and dashes, whereas transformation refers to converting all lowercase letters to uppercase. Both are necessary to achieve the final desired result.

Language Agnostic Coding Drills

  1. String Manipulation (Beginner): The very basis of this problem is string manipulation, where we are replacing one character with another in the string using the replace method. This also includes converting the string to uppercase using the upper method.

  2. List Operations (Beginner): The code involves creating an empty list and appending elements to it. It’s a simple yet crucial part of many algorithms.

  3. Mathematical Operators (Beginner): Understanding the use of the modulus operator is essential for solving this problem. The modulus operator (%) gives the remainder of a division operation, here used to calculate the size of the first group.

  4. Conditional Statements (Intermediate): The code checks a condition (if head is not zero) and executes a block of code based on that condition. Understanding how to write and use conditional statements is key to controlling the flow of the program.

  5. Slicing (Intermediate): Slicing is used to extract a portion of the string. The concept of slicing and understanding how to use it to get a substring from a given string is crucial.

  6. Loops (Intermediate): The code uses a for loop with a start, stop, and step argument in the range function. This is used to iterate over the string in chunks of size k.

  7. Joining Strings (Intermediate): The ‘join’ function is used to convert a list of strings into a single string with a specified delimiter. Understanding how to use this function is important for formatting the output in the required manner.

The problem-solving strategy starts from simple string and list manipulations and goes towards more complex concepts like slicing, looping, and joining strings. Each of these concepts contributes to a part of the solution, and understanding each part will help in understanding how the overall solution works. For example, string manipulations and slicing are used to format the string, looping is used to divide the string into chunks of a specific size, and joining is used to combine these chunks back into a single string.

Targeted Drills in Python

Drill 1 - String Manipulation

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def string_manipulation(s):
    s = s.replace('a', 'b')  # Replace all 'a' in the string with 'b'
    s = s.upper()  # Convert all characters to uppercase
    return s

print(string_manipulation("banana"))  # Output: "BBNBNB"

Drill 2 - List Operations

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def list_operations():
    lst = []  # Create an empty list
    lst.append("apple")  # Add "apple" to the list
    return lst

print(list_operations())  # Output: ["apple"]

Drill 3 - Mathematical Operators

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def mathematical_operators(x, y):
    return x % y  # Return the remainder of x divided by y

print(mathematical_operators(10, 3))  # Output: 1

Drill 4 - Conditional Statements

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def conditional_statements(x):
    if x > 0:
        return "Positive"
    else:
        return "Non-positive"

print(conditional_statements(5))  # Output: "Positive"

Drill 5 - Slicing

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def slicing(s):
    return s[1:3]  # Return the substring from index 1 to 2

print(slicing("Hello"))  # Output: "el"

Drill 6 - Loops

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def loops(s, k):
    for i in range(0, len(s), k):
        print(s[i:i+k])

loops("Hello World", 3)  # Output: "Hel", "lo ", "Wor", "ld"

Drill 7 - Joining Strings

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def joining_strings(lst):
    return '-'.join(lst)

print(joining_strings(["Hello", "World"]))  # Output: "Hello-World"

These drills form the building blocks of the final solution. We start with string manipulation by removing dashes and converting to uppercase. We then calculate the size of the first group and start creating groups. We create the first group only if its size is not zero. We then create subsequent groups using a loop, and finally join all these groups with dashes. All these drills are combined in the final solution as shown below:

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def licenseKeyFormatting(s, k):
    s = s.replace('-', '')  # Drill 1
    s = s.upper()  # Drill 1
    head = len(s) % k  # Drill 3
    grouping = []  # Drill 2

    if head:  # Drill 4
        grouping.append(s[:head])  # Drill 2, 5

    for i in range(head, len(s), k):  # Drill 6
        grouping.append(s[i:i+k])  # Drill 2, 5

    return '-'.join(grouping)  # Drill 7

print(licenseKeyFormatting("5F3Z-2e-9-w", 4))  # Output: "5F3Z-2E9W"