## 1. Question

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.

## 2. Examples

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.


## 3. Constraints

• 1 <= s.length <= 105

• s consists of English letters, digits, and dashes '-'.

• 1 <= k <= 104

## 5. Solutions

class Solution {
public String licenseKeyFormatting(String s, int k) {
s = s.toUpperCase();
StringBuilder sb = new StringBuilder();
int count = 0;
for (int i = s.length() - 1; i >= 0; i--) {
if (s.charAt(i) != '-') {
sb.append(s.charAt(i));
count++;
}
if (count == k) {
sb.append('-');
count = 0;
}
}
if (sb.length() > 0 && sb.charAt(sb.length() - 1) == '-') {
sb.deleteCharAt(sb.length() - 1);
}
return sb.reverse().toString();
}
}