LicenseKeyFormatting482.java

/**
 * 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:
 * 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 LicenseKeyFormatting482 {
    public String licenseKeyFormatting(String S, int K) {
        char[] chars = S.toCharArray();
        
        int i = chars.length - 1;
        int loop = -1;
        StringBuilder sb = new StringBuilder();
        while (i >= 0) {
            if (chars[i] == '-') {
                i--;
                continue;
            }
            sb.append(Character.toUpperCase(chars[i]));
            i--;
            loop = (loop + 1) % K;
            if (loop == K-1) {
                sb.append("-");
            }
        }
        sb = sb.reverse();
        if (sb.length() > 0 && sb.charAt(0) == '-') sb.deleteCharAt(0);
        return sb.toString();
    }

}