题解 | #学英语#

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int num = in.nextInt();
        System.out.println(solution(num));
    }

    private static final String[] base = new String[] {
        "",  "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten",
        "eleven", "twelve", "thirteen", "fourteen", "fifteen",
        "sixteen", "seventeen",
        "eighteen",
        "nineteen", "twenty"
    };

    private static final String[] tenP = new String[] {
        "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"
    };
    private static String solution(int num) {
        if (num <= 20) {
            return base[num];
        }
        if (num < 100) {
            return tenP[num / 10 - 2] + ((num % 10 != 0) ? " " + solution(num % 10) : "");
        }
        if (num < 1_000) {
            return base[num / 100] + " hundred" + (num % 100 != 0 ? " and " + solution(
                    num % 100) : "");
        }
        if(num < 1_000_000) {
            return solution(num / 1000) + " thousand" + (num % 1000 != 0 ? " " + solution(num % 1000) : "");
        }
        if(num < 1_000_000_000) {
            return solution(num / 1_000_000) + " million" +  (num % 1_000_000 != 0 ? " " + solution(num % 1_000_000) : "");
        }
        return solution(num / 1_000_000_000) + " billion" + (num % 1_000_000_000 != 0 ? " " + solution(num % 1_000_000_000) : "");
    }
}