## 482. License Key Formatting

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.

## Rust Solution

``````struct Solution;

impl Solution {
fn license_key_formatting(s: String, k: i32) -> String {
let mut res: Vec<char> = vec![];
let mut i = 0;
for c in s.chars().rev() {
if c != '-' {
res.push(c);
i += 1;
if i == k {
i = 0;
res.push('-');
}
}
}
if let Some(&'-') = res.last() {
res.pop();
}
res.iter().rev().collect::<String>().to_ascii_uppercase()
}
}

#[test]
fn test() {
let s = "5F3Z-2e-9-w".to_string();
let k = 4;
let o = "5F3Z-2E9W".to_string();
assert_eq!(Solution::license_key_formatting(s, k), o);

let s = "2-5g-3-J".to_string();
let k = 2;
let o = "2-5G-3J".to_string();
assert_eq!(Solution::license_key_formatting(s, k), o);
}
``````

Having problems with this solution? Click here to submit an issue on github.