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();

    }

}

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