题解 | #学英语#

import java.util.HashMap;
import java.util.Scanner;

public class Main {
    private static final HashMap<Integer, String> numEngMap = new HashMap<Integer, String>(){{
        put(1, "one");
        put(2, "two");
        put(3, "three");
        put(4, "four");
        put(5, "five");
        put(6, "six");
        put(7, "seven");
        put(8, "eight");
        put(9, "nine");
        put(10, "ten");
        put(11, "eleven");
        put(12, "twelve");
        put(13, "thirteen");
        put(14, "fourteen");
        put(15, "fifteen");
        put(16, "sixteen");
        put(17, "seventeen");
        put(18, "eighteen");
        put(19, "nineteen");
        put(20, "twenty");
        put(30, "thirty");
        put(40, "forty");
        put(50, "fifty");
        put(60, "sixty");
        put(70, "seventy");
        put(80, "eighty");
        put(90, "ninety");
        put(100, "hundred");
    }};

    public static void main(String[] args){
        Scanner in = new Scanner(System.in);

        while(in.hasNext()){
            solution(in);
        }
    }

    /**
     * 模拟法
     * @param in
     */
    private static void solution(Scanner in){
        long number = in.nextLong();

        String numStr = String.valueOf(number);
        int numStrLen = numStr.length();
        int times = numStrLen / 3;
        int remainder = numStrLen % 3;

        String[] units = new String[]{"", "thousand", "million", "billion"};
        StringBuilder result = new StringBuilder();

        // 从右到左 每3位数转换一次
        for(int i=1; i<=times; i++){
            result.insert(0, numToEng(Integer.parseInt(numStr.substring(numStrLen-i*3, numStrLen-(i-1)*3)))+units[i-1]+" ");
        }
        if(remainder > 0){
            if(times == 0){
                result.insert(0, numToEng(Integer.parseInt(numStr.substring(0, remainder))));
            }else{
                result.insert(0, numToEng(Integer.parseInt(numStr.substring(0, remainder)))+units[times]+" ");
            }
        }

        System.out.println(result);
    }

    /**
     * 三位数 转 英文
     * @param num
     * @return
     */
    private static String numToEng(int num){
        StringBuilder sb = new StringBuilder();

        // 百位
        int hundredthDigit = num / 100;
        int hundredthRemainder = num % 100;
        if(hundredthDigit > 0){
            sb.append(numEngMap.get(hundredthDigit) + " " + numEngMap.get(100) + " ");
            if(hundredthRemainder > 0){
                sb.append("and ");
            }
        }

        // 十位及个位
        if(hundredthRemainder > 0){
            int tenthDigit = hundredthRemainder / 10;
            int tenthRemainder = hundredthRemainder % 10;
            // 10 20 30 40 50 60 70 80 90
            if(tenthRemainder == 0){
                sb.append(numEngMap.get(hundredthRemainder)).append(" ");
            }else{
                // 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19
                if(tenthDigit <= 1){
                    sb.append(numEngMap.get(hundredthRemainder)).append(" ");
                }else{
                    sb.append(numEngMap.get(tenthDigit*10)).append(" ");
                    sb.append(numEngMap.get(tenthRemainder)).append(" ");
                }
            }
        }

        return sb.toString();
    }
}