"""
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.

"""

class Solution:
    def licenseKeyFormatting(self, S: str, K: int) -> str:
        original = S.replace('-','').upper()
        reformat_list = []
        length = len(original)
        for i in range(int(length/K) + 1):
            current = original[max(0, length-(i+1)*K):length-i*K]
            if current:
                reformat_list.insert(0, current)
        return '-'.join(reformat_list)

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