题解 | #学英语#

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNextLong()) { 
            long num = in.nextLong();
            if (num > 999) {
                String out = getNumEngExp(num);
                if(out.endsWith(" and ")) {
                    System.out.println(out.substring(0, out.length()-4));
                } else {
                    System.out.println(out);
                }
                
            } else {
                String out = num1To999(num);
                if(out.endsWith(" and ")) {
                    System.out.println(out.substring(0, out.length()-4));
                } else {
                    System.out.println(out);
                }
            }
        }
    }

    public static String num1To19(long num) {
        if (num < 1 || num > 19) {
            return "";
        }
        String[] names = {
                "one ", "two ", "three ", "four ", "five ", "six ", "seven ", "eight ","nine ",
                "ten ", "eleven ", "twelve ", "thirteen ", "fourteen ", "fifteen ", "sixteen ", "seventeen ",
                "eighteen ", "nineteen "
        };
        return names[(int)num-1];
    }

    public static String num1To99(long num) {
        if (num < 1 || num > 99) {
            return "";
        }
        if (num < 20) {
            return num1To19(num);
        }
        long high = num /10;
        String[] tyNames = {
                "twenty ", "thirty ", "forty ", "fifty ", "sixty ",
                "seventy ", "eighty ", "ninety "
        };
        return tyNames[(int)high-2] + num1To19(num % 10);
    }

    public static String num1To999(long num) {
        if (num < 1 || num > 999) {
            return "";
        }
        if (num < 100) {
            return num1To99(num);
        }
        long high = num /100;
        return num1To19(high) + "hundred and " + num1To99(num % 100);
    }

    public static String getNumEngExp(long num) {
        if (num == 0) {
            return "zero";
        }
        String res = "";
        if (num < 0) {
            res = "negative, ";
        }
        if (num == Long.MIN_VALUE) {
            res += "two billion, ";
            num %= -2 * 1000 * 1000 * 1000;
        }
        num = Math.abs(num);
        long high = 1 * 1000 * 1000 * 1000;
        int highIndex = 0;
        String[] names = {"billion", "million", "thousand"};
        while (num != 0) {
            long cur = num / high;
            num %= high;
            if (cur != 0) {
                res += num1To999(cur);
                if (highIndex < 3) {
                    res += names[highIndex] + " ";
                }
            }
            high /= 1000;
            highIndex++;
        }
        return res;
    }
}