482. License Key Formatting 格式化激活码

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.

/**
 * @param {string} S
 * @param {number} K
 * @return {string}
 */
var licenseKeyFormatting = function (S, K) {
    let res = "";
    let str = S.replace(/-/g, "");
    let groupLength = 0;
    for (let i = str.length - 1; i >= 0; i--) {
        res = str[i].toUpperCase() + res;
        if (++groupLength == K && i != 0) {
            res = "-" + res;
            groupLength = 0;
        }
    }
    return res;
};


let s = "2-5g-3-J";
let k = 2;
let res = licenseKeyFormatting(s, k);
console.log(res);

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