482. License Key Formatting

Description

You are given a license key represented as a string s that consists of only alphanumeric characters and dashes. The string is separated into n + 1 groups by n dashes. You are also given an integer k.

We want to reformat the string s such that each group contains exactly k characters, except for the first group, which could be shorter than k but still must contain at least one character. Furthermore, there must be a dash inserted between two groups, and you should convert all lowercase letters to uppercase.

Return the reformatted license key.

Example 1:

Input: s = "5F3Z-2e-9-w", k = 4
Output: "5F3Z-2E9W"
Explanation: The string s has been split into two parts, each part has 4 characters.
Note that the two extra dashes are not needed and can be removed.

Example 2:

Input: s = "2-5g-3-J", k = 2
Output: "2-5G-3J"
Explanation: The string s has been split into three parts, each part has 2 characters except the first part as it could be shorter as mentioned above.

Constraints:

1 <= s.length <= 10⁵
s consists of English letters, digits, and dashes '-'.
1 <= k <= 10⁴

Solution

license-key-formatting.py

class Solution:
    def licenseKeyFormatting(self, s: str, k: int) -> str:
        s = s.split('-')
        words = "".join(s)
        n = len(words)

        M = n % k
        start = M if M != 0 else k
        res = []
        res.append(words[:start].upper())

        for i in range(start, n, k):
            res.append(words[i : min(n, i + k)].upper())

        return "-".join(res)