Java实现 LeetCode 273 整数转换英文表示

273. 整数转换英文表示

将非负整数转换为其对应的英文表示。可以保证给定输入小于 231 - 1 。

示例 1:

输入: 123
输出: “One Hundred Twenty Three”
示例 2:

输入: 12345
输出: “Twelve Thousand Three Hundred Forty Five”
示例 3:

输入: 1234567
输出: “One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven”
示例 4:

输入: 1234567891
输出: “One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One”

class Solution {
       final static String[] zeroToNineteen = {"Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine",
                                        "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen",
                                        "Eighteen", "Nineteen"};
    final static String[] twentyToNinety = {"Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
    final int BILLION = 1000000000;
    final int MILLION = 1000000;
    final int THOUSAND = 1000;
    final int HUNDRED = 100;
    public String numberToWords(int num) {
         if (num == 0) return "Zero";
        StringBuilder builder = new StringBuilder();
        if (num >= BILLION) {
            if (builder.length() != 0) builder.append(" ");
            builder.append(numberToWords(num / BILLION)).append(" Billion");
            num %= BILLION;
        }
        if (num >= MILLION) {
            if (builder.length() != 0) builder.append(" ");
            builder.append(numberToWords(num / MILLION)).append(" Million");
            num %= MILLION;
        }
        if (num >= THOUSAND) {
            if (builder.length() != 0) builder.append(" ");
            builder.append(numberToWords(num / THOUSAND)).append(" Thousand");
            num %= THOUSAND;
        }
        if (num >= HUNDRED) {
            if (builder.length() != 0) builder.append(" ");
            builder.append(numberToWords(num / HUNDRED)).append(" Hundred");
            num %= HUNDRED;
        }
        if (num < 20) {
            if (num != 0) {
                if (builder.length() != 0) builder.append(" ");
                builder.append(zeroToNineteen[num]);
            }
        }
        else {
            if (builder.length() != 0) builder.append(" ");
            builder.append(twentyToNinety[num / 10 - 2]);
            if (num % 10 != 0) {
                if (builder.length() != 0) builder.append(" ");
                builder.append(zeroToNineteen[num % 10]);
            }
        }
        return builder.toString();
    }
}