## Description

https://leetcode.com/problems/license-key-formatting/

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.

Return *the reformatted license key*.

**Example 1:**

Input:s = "5F3Z-2e-9-w", k = 4Output:"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 = 2Output:"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 <= 10`

^{5}`s`

consists of English letters, digits, and dashes`'-'`

.`1 <= k <= 10`

^{4}

## Explanation

Iterate the characters from the string backward and add a ‘-‘ whenever the count is a multiple of k.

## Python Solution

```
class Solution:
def licenseKeyFormatting(self, s: str, k: int) -> str:
s = s.replace('-', '')
results = []
count = 0
for c in s[::-1]:
if count != 0 and count % k == 0:
results.insert(0, '-')
results.insert(0, c.upper())
count += 1
return "".join(results)
```

- Time Complexity: O(N).
- Space Complexity: O(N).