杭电acm1013 Digital Roots 数字根 Java解法 高精度

import java.math.BigInteger;
import java.util.Scanner;
 
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        BigInteger i;
        while (!(i = sc.nextBigInteger()).equals(BigInteger.ZERO)) {
            BigInteger sum = BigInteger.ZERO;
            while (i.compareTo(BigInteger.ZERO) > 0) {
                sum = sum.add(i.mod(BigInteger.TEN));
                i = i.divide(BigInteger.TEN);
            }
            while (sum.compareTo(BigInteger.TEN) >= 0) {
                i = sum;
                sum = BigInteger.ZERO;
                while (i.compareTo(BigInteger.ZERO) > 0) {
                    sum = sum.add(i.mod(BigInteger.TEN));
                    i = i.divide(BigInteger.TEN);
                }
            }
            System.out.println(sum);
        }
    }
}