How do you solve License Key Formatting on LeetCode?

License Key Formatting (LeetCode #482) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Removing dashes and converting to uppercase are essential preprocessing steps.

What is the brute force solution for License Key Formatting?

The brute force approach for License Key Formatting is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves cleaning the string by removing dashes and then manually constructing the formatted license key by iterating through the characters. This method is straightforward but inefficient for larger strings. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve License Key Formatting?

License Key Formatting uses the following concepts: String. The recommended patterns to study are: String Manipulation, Two Pointers.

What are the interview tips for License Key Formatting?

Always clarify the input format and constraints. Discuss edge cases, such as strings with only dashes. Explain your thought process as you code.

What are common mistakes when solving License Key Formatting?

Forgetting to handle the first group size correctly. Not converting characters to uppercase before processing.

#482

License Key Formatting

Easy

StringString ManipulationTwo Pointers

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

The optimal approach efficiently formats the license key by iterating through the cleaned string in reverse, building the result directly. This minimizes the number of operations and avoids unnecessary string manipulations.

⚙️

Algorithm

4 steps

1Step 1: Remove dashes and convert to uppercase.
2Step 2: Initialize an empty result string and a counter for characters.
3Step 3: Iterate through the cleaned string in reverse, adding characters to the result.
4Step 4: Insert dashes every k characters, except for the first group.

solution.py10 lines

1def licenseKeyFormatting(s: str, k: int) -> str:
2    s = s.replace('-', '').upper()
3    result = []
4    count = 0
5    for char in reversed(s):
6        if count > 0 and count % k == 0:
7            result.append('-')
8        result.append(char)
9        count += 1
10    return ''.join(reversed(result))

ℹ

Complexity note: This approach runs in O(n) time because we make a single pass through the string and build the result in linear time. The space complexity is O(n) due to the storage of the result string.

1Removing dashes and converting to uppercase are essential preprocessing steps.
2Iterating from the end allows for easier group formation.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.