java - 随机取一个整数，进行拆分，拆分后相加合大于9的话继续拆，直到小于9。

Question

java实现 新手，用字符串拆分怎么实现？
比如100拆成1，0,0 相加大于9的话就继续拆，小于9就输出

Answer 1

Just output the number modulo 9

---

Proof:

Suppose the number is:

$$m=a_na_{n-1}ldots a_0$$

then

$$m=sum^n_{i=0}a_itimes10^i$$
$$=sum^n_{i=0}a_itimes(99dots9+1)$$
$$equivsum^n_{i=0}a_i (mod 9)$$

Answer 2

This is the original question on leetcode...
Just take the modulo of 9

Answer 3

This uses a direct method and doesn’t feel difficult.

/**
 * Created by weixuan on 16/6/5.
 */
public class Test {

    // 第一步 to char

    public static char[] toChar(Integer data) {
        String value = String.valueOf( data );
        return value.toCharArray();
    }

    // 相加
    public static Integer add(char[] data) {
        Integer sum = 0;
        for (char d : data) {
            sum += d - '0';
        }
        return sum;
    }

    // 判断是否大于9
    public static Integer isBiggerCore(Integer data) {
        return add( toChar( data ) );
    }

    public static Integer isBigger(Integer data) {
        int value = data;
        int temp = isBiggerCore( data );
        while (temp > 9) {
            value = temp;
            temp = isBiggerCore( value );
        }
        return value;
    }

    // 987 -> 24
    // 99 -> 18
    // 199 -> 10
    public static void main(String[] args) {

        System.out.println(isBigger( 987 ));
    }
}