LicenseKeyFormatting.js

// Source : https://leetcode.com/problems/license-key-formatting
// Author : Dean Shi
// Date   : 2017-02-25

/***************************************************************************************
 *
 * Now you are given a string S, which represents a software license key which we would
 * like to format. The string S is composed of alphanumerical characters and dashes.
 * The dashes split the alphanumerical characters within the string into groups. (i.e.
 * if there are M dashes, the string is split into M+1 groups). The dashes in the given
 * string are possibly misplaced.
 *
 * We want each group of characters to be of length K (except for possibly the first
 * group, which could be shorter, but still must contain at least one character). To
 * satisfy this requirement, we will reinsert dashes. Additionally, all the lower case
 * letters in the string must be converted to upper case.
 *
 * So, you are given a non-empty string S, representing a license key to format, and an
 * integer K. And you need to return the license key formatted according to the
 * description above.
 *
 * Example 1:
 *
 * Input: S = "2-4A0r7-4k", K = 4
 *
 * Output: "24A0-R74K"
 *
 * Explanation: The string S has been split into two parts, each part has 4 characters.
 *
 * Example 2:
 *
 * Input: S = "2-4A0r7-4k", K = 3
 *
 * Output: "24-A0R-74K"
 *
 * Explanation: The string S has been split into three parts, each part has 3
 * characters except the first part as it could be shorter as said 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) {
    let result = ''
    for (let i = S.length - 1; i >= 0; i--) {
        if (S[i] !== '-') {
            result = S[i] + (result.length % (K+1) === K ? '-' : '') + result
        }
    }
    return result.toUpperCase()
};