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.

class Solution {

public:

    string licenseKeyFormatting(string S, int K) {

        string res;

        

        int count = 0;

        for (auto it = S.rbegin() ; it != S.rend(); ++it)

        {

            if (*it != '-')

            {

                res += toupper((*it));

                if (++count == K)

                {

                    res +='-';

                    count = 0;

                }

            }

        }

        if (res.empty()) {

            return res;

        }

        

        if (res.back() == '-') res.pop_back();

        

        reverse(res.begin(), res.end());

        

        return res;

    }

};

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string licenseKeyFormatting(string S, int K) { int c = 0; string ret = ""; ret.reserve(S.size()); for(auto itr = S.rbegin(); itr != S.rend(); ++itr) { if(*itr == '-') continue; if(c == K) { c = 0; ret.push_back('-'); } ret.push_back(toupper(*itr)); ++c; } reverse(ret.begin(), ret.end()); return ret; }