LicenseKeyFormatting.java

package easy;
/**
 * ClassName: LicenseKeyFormatting.java
 * Author: chenyiAlone
 * Create Time: 2019/11/13 20:54
 * Description: No.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:
 * 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 LicenseKeyFormatting {
    
    public String licenseKeyFormatting(String S, int K) {
        StringBuilder ret = new StringBuilder();
        for (int i = S.length() - 1, cnt = 0; i >= 0; i--) {
            char c = S.charAt(i);
            if (c != '-') {
                if (cnt == K) {
                    ret.append('-');
                    cnt = 0;
                }
                ret.append((char)('a' <= c && c <= 'z' ? (c - 32) : c));
                cnt++;
            }
        }
        return ret.reverse().toString();
    }
    
}