// 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:
// The length of string S will not exceed 12,000, and K is a positive integer.
//     String S consists only of alphanumerical characters (a-z and/or A-Z and/or 0-9) and dashes(-).
//     String S is non-empty.

/**
 * @param {string} S
 * @param {number} K
 * @return {string}
 */
var licenseKeyFormatting = function(S, K) {
    var raw = S.replace(/-/g, ''). toUpperCase();
    var length = raw.length;
    var arr = [];
    while (length > 0) {
        arr.push(raw.substring(length - K, length));
        length -= K;
    }
    return arr.reverse().join('-');
};

console.log(licenseKeyFormatting("5F3Z-2e-9-w", 4));
console.log(licenseKeyFormatting("2-5g-3-J", 2));
console.log(licenseKeyFormatting("r", 1));
console.log(licenseKeyFormatting("a-a-a-a-", 1));
console.log(licenseKeyFormatting("0123456789", 1));
console.log(licenseKeyFormatting("---", 3));