integerToEnglish.txt

273. Integer to English Words

Convert a non-negative integer num to its English words representation.

class Solution {
public:
    string ones[20] = {"", " One", " Two", " Three", " Four", " Five", " Six", " Seven", " Eight", " Nine", " Ten", " Eleven", " Twelve", " Thirteen", " Fourteen", " Fifteen", " Sixteen", " Seventeen", " Eighteen", " Nineteen"};
    string tens[10] = {"", " Ten", " Twenty", " Thirty", " Forty", " Fifty", " Sixty", " Seventy", " Eighty", " Ninety"};
    string thousands[4] = {"", " Thousand", " Million", " Billion"};

    string helper(int num){
        if(num < 20) return ones[num];
        if(num < 100) return tens[num/10] + helper(num % 10);
        if(num < 1000) return helper(num/100) + " Hundred" + helper(num % 100);
        for(int i = 3 ; i >= 0 ; i--){
            if(num >= pow(1000,i)){
                return helper(num/pow(1000,i))+thousands[i]+helper(num%(int)pow(1000,i));
            }
        }
        return "";
    }

    string numberToWords(int num) {
        if(num == 0) return "Zero";
        return helper(num).substr(1);
    }
};