Formatted question description:

482. License Key Formatting




You are given a license key represented as a string S which consists only alphanumeric character and dashes. The string is separated into N+1 groups by N dashes.

Given a number K, we would want to reformat the strings 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 all lowercase letters should be converted to uppercase.

Given a non-empty string S and a number K, format the string according to the rules described above.

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.


  1. The length of string S will not exceed 12,000, and K is a positive integer.
  2. String S consists only of alphanumerical characters (a-z and/or A-Z and/or 0-9) and dashes(-).
  3. String S is non-empty.


First turn all the letters in S to upper case and remove all dashes from S. Then loop over S from right to left and add a dash before every K characters. Finally, return the new string.

  • class Solution {
        public String licenseKeyFormatting(String S, int K) {
            S = S.toUpperCase();
            S = S.replaceAll("-", "");
            int length = S.length();
            StringBuffer sb = new StringBuffer(S);
            int count = 0;
            for (int i = length - 1; i > 0; i--) {
                if (count == K) {
                    sb.insert(i, '-');
                    count = 0;
            return sb.toString();
  • Todo
  • class Solution(object):
      def licenseKeyFormatting(self, S, K):
        :type S: str
        :type K: int
        :rtype: str
        s = S.split("-")
        s = "".join(s)
        n = len(s)
        start = n % K
        res = []
        if start != 0:
        for k in range(0, (len(s) - start) / K):
          res.append(s[start:start + K].upper())
          start += K
        return "-".join(res)

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