#### QUESTION:

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

#### SOLUTION:

``````class Solution {
public String licenseKeyFormatting(String S, int K) {
Stack<Character> stack = new Stack<>();
for(char c: S.toCharArray()){
if(c=='-') continue;
}

int index = 0;
StringBuilder sb = new StringBuilder();
while (!stack.isEmpty()){
Character pop = stack.pop();
sb.insert(0,pop);
index++;
if(index==K && !stack.isEmpty()){
sb.insert(0,'-');
index=0;
}
}
return sb.toString().toUpperCase();
}
}
``````