算法：数字转换，例如10086转换为“10000+80+6”，123654转换为“100000+20000+3000+600+50+4”

数字转换，例如10086转换为“10000+80+6”，123654转换为“100000+20000+3000+600+50+4”

import java.math.BigDecimal;
import java.util.*;
import java.util.stream.Collectors;

/**
 * @Author zlf
 * @Date 2020/6/22 9:54
 * @Version 1.0
 * @Description
 */
public class StringTest {
    public static void main(String[] args){
        System.out.println(Test(10086));
    }

    public static String Test(Integer x){
        String s = x.toString();
        char[] chars = s.toCharArray();
        int length = s.length();
        StringBuilder stringBuilder=new StringBuilder();
        HashMap<Integer,Character> values=new HashMap<>();
        for (int i = 0; i <length; i++) {
            values.put(i,chars[length-1-i]);
        }
        List<BigDecimal> list =new ArrayList<>();
        System.out.println(values.toString());
        for (Map.Entry<Integer, Character> entry :values.entrySet()) {
            double value = Double.parseDouble(entry.getValue().toString());
            BigDecimal a2 = new BigDecimal(value);
            if (!a2.equals(BigDecimal.ZERO)){
                double pow = Math.pow(10.0, entry.getKey());
                BigDecimal a1 = new BigDecimal(pow);
                BigDecimal multiply = a1.multiply(a2);
                list.add(multiply);
            }

        }
        list = list.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
        for (int i=0;i<list.size()-1;i++){
            stringBuilder.append(list.get(i)+"+");
        }
        stringBuilder.append(list.get(list.size()-1));
        System.out.println(list.toString());
        return  stringBuilder.toString();
    }
}

方法二效率提升一点点

package ApiTest;

import java.math.BigDecimal;
import java.util.*;
import java.util.stream.Collectors;

/**
 * @Author zlf
 * @Date 2020/6/24 11:02
 * @Version 1.0
 * @Description
 */
public class StringTest2 {
    public static void main(String[] args){
    System.out.println(Test(123654));
}

    public static String Test(Integer x){
        String s = x.toString();
        List<String> newList=new ArrayList<>();
        List<BigDecimal> list =new ArrayList<>();
        StringBuilder stringBuilder=new StringBuilder();
        for(int i=s.length()-1;i>=0;i--){
            newList.add(s.substring(i,i+1));
            System.out.println(s.substring(i,i+1));
        }
        for (int i=0;i<newList.size();i++){
            String s1 = newList.get(i);
            BigDecimal a2 = new BigDecimal(s1);
            if (!a2.equals(BigDecimal.ZERO)){
                double pow = Math.pow(10.0, new Double(i));
                BigDecimal a1 = new BigDecimal(pow);
                BigDecimal multiply = a1.multiply(a2);
                list.add(multiply);
            }

        }
        list = list.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
        for (int i=0;i<list.size()-1;i++){
            stringBuilder.append(list.get(i)+"+");
        }
        stringBuilder.append(list.get(list.size()-1));
        System.out.println(list.toString());
        return  stringBuilder.toString();
    }
}