## DEV Community

Abhishek Chaudhary

Posted on

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.

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.

Constraints:

• `1 <= s.length <= 105`
• `s` consists of English letters, digits, and dashes `'-'`.
• `1 <= k <= 104`

SOLUTION:

``````class Solution:
def licenseKeyFormatting(self, s: str, k: int) -> str:
op = []
n = len(s)
i = 0
for c in range(n - 1, -1, -1):
if s[c] != "-":
i += 1
op.append(s[c].upper())
if i % k == 0:
op.append("-")
if len(op) > 0 and op[-1] == "-":
op.pop()
op.reverse()
return "".join(op)
``````