482. License Key Formatting

• Difficulty: Easy

• Topics:

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Problem:

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:

Solutions:

class Solution {
public:
    string licenseKeyFormatting(string S, int K) {
        string ret;
        int count = 0;
        if (S.length() == 0)    return "";
        for (int i = S.length() - 1; i >= 0; --i) {
            if (S[i] == '-')    continue;
            ret.push_back(toupper(S[i]));
            ++count;
            if (count == K) {
                ret.push_back('-');
                count = 0;
            }    
        }

        if (ret.back() == '-')  ret.pop_back();
        return {ret.rbegin(), ret.rend()};
    }
};