Formatted question description: https://leetcode.ca/all/482.html

Easy

## Description

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.

Note:

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.

## Solution

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--) {
count++;
if (count == K) {
sb.insert(i, '-');
count = 0;
}
}
return sb.toString();
}
}