You are given a license key represented as a string S which consists of 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: 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.
public class Solution {
public string LicenseKeyFormatting(string S, int K) {
var sb = new StringBuilder();
for(int i=S.Length-1,j=0;i>=0;i--){
if(S[i]!='-'){
if(j!=0 && j%K==0){
sb.Append("-");
}
sb.Append(S[i]);
j++;
}
}
return new string(sb.ToString().ToUpper().Reverse().ToArray());
}
}Time Complexity: O(n)
Space Complexity: O(n)
