/**

* 将字符串s按长度k为一组，从右往左重排，组之间用"-"分隔，还要转成大写

* 注意别在最前面多加一个"-"，即下面判断i != 0

*/

public class LicenseKeyFormatting {

// 耗时13ms

public String licenseKeyFormatting(String S, int K) {

StringBuilder sb = new StringBuilder();

for (int i = S.length() - 1, j = 0; i >= 0; i--) {

if (S.charAt(i) != '-') {

if (j % K == 0 && sb.length() > 0) {

sb.append("-");

}

sb.append(Character.toUpperCase(S.charAt(i)));

j++;

}

}

return sb.reverse().toString();

}

}