Leetcode•Jul 22, 2025
License Key Formatting
Hazrat Ali
Leetcode
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 = 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.
Solution
/**
* @param {string} s
* @param {number} k
* @return {string}
*/
const licenseKeyFormatting = (s, k) => {
let key = '';
for (let c of reverse(s)) {
if (c !== '-') {
if (key.length % (k + 1) === k) {
key += '-';
}
key += c.toUpperCase();
}
}
return reverse(key);
};
const reverse = str => [...str].reverse().join('');