動機

不要忘了reverse很好用

Problem

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 = 4Output: "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 = 2Output: "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

Sol

從最後一個字去分組，最後再reverse

class Solution:
    def licenseKeyFormatting(self, s: str, k: int) -> str:
        cs = [c for c in s if c != "-"][::-1]
        ss = []
        i = 0
        while i < len(cs):
            tmp = []
            for _ in range(k):
                if i < len(cs):
                    tmp += cs[i].upper(),
                    i += 1
                else:
                    break
            if tmp:
                ss += ''.join(tmp),
        return '-'.join(ss)[::-1]