273 Integer to English Words 整数转换英文表示

将非负整数转换为其对应的英文表示，给定的输入是保证小于 2³¹ - 1 的。
示例：
123 -> "One Hundred Twenty Three"
12345 -> "Twelve Thousand Three Hundred Forty Five"
1234567 -> "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

详见：https://leetcode.com/problems/integer-to-english-words/description/

Java实现：

每三位数一读。每读三位数的时候在三位数后面加上单位（Thousand, Million, or Billion）即可。其中的关键点是当读取的三位数是“0”，那么后面的单位就要舍弃。比如1000000，读第二个三位数是“000”，那么对应的单位Thousand是要舍弃的，否则就会变成One Million Thousand的错误结果。

class Solution {

    //全局变量先把要用的英文存起来

    String[] units = {"", " Thousand", " Million", " Billion"};

    String[] num0To9 = {"Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"};

    String[] num10To19 = {"Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};

    String[] num10To90 = {"Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};

    public String numberToWords(int num) {

        if (num == 0){

            return "Zero";

        }

        String res = "";

        int count = 0; //记录当前三位数下后面跟的单位

        while (num > 0) {

            String tmp = "";

            tmp = units[count]; //记录当前三位数下后面跟的单位

            int cur = num % 1000; //每三位一读，从后往前

            String pre = convert(cur); //转化当前数字最后的三位数

            if (pre == ""){

                tmp = ""; //如果是"000"，那么就等于什么都没发生，舍弃单位

            }else{

                tmp = convert(cur) + tmp; //否则结合结果和单位

            }

            if (res.length() != 0 && res.charAt(0) != ' '){ //处理一下加上单位的空格情况

                res = tmp + " " + res;

            }else{

                res = tmp + res;

            }

            num = (num - num % 1000) / 1000; //处理往前三位数

            count++;

        }

        return res;

    }

    //转化任意三位数

    public String convert(int num) {

        if (num == 0){

            return "";

        }

        if (num < 10){

            return num0To9[num];

        }else if (num >= 10 && num <= 19){

            return num10To19[num - 10];

        }else if (num >= 20 && num <= 99) {

            if (num % 10 == 0){

                return num10To90[num / 10 - 1];

            }else{

                String s1 = num0To9[num%10];

                String s2 = num10To90[num/10 - 1];

                return s2 + " " + s1;

            }

        }

        else {

            if (num % 100 == 0){

                return num0To9[num / 100] + " Hundred";

            }else {

                String tmp = convert(num % 100);

                return convert(num - num % 100) + " " + tmp;

            }

        }

    }

}

C++实现：

class Solution {

public:

    string numberToWords(int num) {

        string res = convertHundred(num % 1000);

        vector<string> v = {"Thousand", "Million", "Billion"};

        for (int i = 0; i < 3; ++i)

        {

            num /= 1000;

            res = num % 1000 ? convertHundred(num % 1000) + " " + v[i] + " " + res : res;

        }

        while (res.back() == ' ')

        {

            res.pop_back();

        }

        return res.empty() ? "Zero" : res;

    }

    string convertHundred(int num) {

        vector<string> v1 = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};

        vector<string> v2 = {"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};

        string res;

        int a = num / 100, b = num % 100, c = num % 10;

        res = b < 20 ? v1[b] : v2[b / 10] + (c ? " " + v1[c] : "");

        if (a > 0)

        {

            res = v1[a] + " Hundred" + (b ? " " + res : "");

        }

        return res;

    }

};

参考：https://www.cnblogs.com/grandyang/p/4772780.html

273 Integer to English Words 整数转换英文表示的相关教程结束。