Integer to English Words -- leetcode

Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1.

For example,

123 -> "One Hundred Twenty Three"12345 -> "Twelve Thousand Three Hundred Forty Five"1234567 -> "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

基本思路：

需要特殊处理的基本数字是，1~19，

然后就是整十，如，20，30，40，，，90

然后要注意是空格的添加。

class Solution {public:    string numberToWords(int num) {        if (!num)            return "Zero";        return numberToEnglish(num).substr(1);    }        string numberToEnglish(int num) {        static const char *oneTo19Map[] =             {"", "One", "Two", "Three", "Four",            "Five", "Six", "Seven", "Eight",            "Nine", "Ten", "Eleven", "Twelve",            "Thirteen", "Fourteen", "Fifteen", "Sixteen",            "Seventeen", "Eighteen", "Nineteen"};        static const char *tensMap[] =             {"", "", "Twenty", "Thirty", "Forty", "Fifty",            "Sixty", "Seventy", "Eighty", "Ninety"};        if (num >= 1000000000)            return numberToEnglish(num / 1000000000) + " Billion" + numberToEnglish(num % 1000000000);        else if (num >= 1000000)            return numberToEnglish(num / 1000000) + " Million" + numberToEnglish(num % 1000000);        else if (num >= 1000)            return numberToEnglish(num / 1000) + " Thousand" + numberToEnglish(num % 1000);        else if (num >= 100)            return numberToEnglish(num / 100) + " Hundred" + numberToEnglish(num % 100);        else if (num >= 20)            return string(" ") + tensMap[num/10] + numberToEnglish(num % 10);        else if (num)            return string(" ") + oneTo19Map[num];        else            return "";    }};

最后将自己的第一版也贴上作个纪念：

class Solution {public:    string numberToWords(int num) {        const char *thousandsMap[] = {"", " Thousand", " Million", " Billion"};        int base = 1;        int index = 0;        while (num / base >= 1000) {            ++index;            base *= 1000;        }        string ans;        while (base) {            string item = numberToWordsUnit(num / base);            if (!item.empty()) {                if (!ans.empty())                    ans.push_back(' ');                ans += item + thousandsMap[index];            }            num %= base;            base /= 1000;            --index;        }        return ans.empty() ? "Zero" : ans;    }        string numberToWordsUnit(int num) {        const char *OneTo19[] =             {"Zero", "One", "Two", "Three", "Four",            "Five", "Six", "Seven", "Eight",            "Nine", "Ten", "Eleven", "Twelve",            "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen",            "Eighteen", "Nineteen"};        const char *decadeMap[] =             {"Zero", "Ten", "Twenty", "Thirty", "Forty", "Fifty",            "Sixty", "Seventy", "Eighty", "Ninety"};        string ans;        const int hundred = num / 100;        num %= 100;        if (hundred)            ans += string(OneTo19[hundred]) + " Hundred";        if (!num)            return ans;        if (!ans.empty())            ans.push_back(' ');        if (num < 20) {            ans += OneTo19[num];        }        else {            const int decade = num / 10;            num %= 10;            ans += decadeMap[decade];            if (!num)                return ans;            if (!ans.empty())                ans.push_back(' ');            ans += OneTo19[num];        }        return ans;    }};