LeetCode 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.

 

First Attempt: 

 

 

 

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class Solution {     public String licenseKeyFormatting(String S, int K) {                             if(S==null || S.length()==0){                           return null;         }                   String result = "";                   String[] tmp = S.split("-");                   String res = "";                   int sum = 0;         for(int i = 0; i<tmp.length; i++){                           sum = sum+ tmp[i].length();                           res = res + tmp[i].toUpperCase();         }                             int i = sum % K;                   int k = sum/K ;                   //res = res.toUpperCase();                   result = result +  res.substring(0,i);                   if(i!=0 && k!=0){             result = result +"-";         }                             String tmp_res = res.substring(i,res.length());            //System.out.println(sum + " "+ i+" c "+ tmp_res+" d "+ k);                   for(int j = 1; j<= k; j++ ){                                   result = result + tmp_res.substring(K*(j-1), K*j);                               if(j != k ){                                   result = result +"-";             }             // System.out.println( tmp_res.substring(K*(j-1), K*j));         }                   return result;     } }

　　

 

Accepted 

class Solution {
    public String licenseKeyFormatting(String S, int K) {
        
        
        if(S==null || S.length()==0){
            
            return null;
        }
        
     
        
        S = S.replaceAll("[-]", "");
        S = S.toUpperCase();
                
        
        StringBuilder sb = new StringBuilder();
        sb.append(S);

        int i=sb.length()-K;
        
        while(i>0) {
            sb.insert(i, '-');
            i = i-K;
        }

        
        return sb.toString();
    }
}