Leetcode 273: Integer to English Words

leetcode_273.cpp

#include <iostream>
#include <string>
#include <vector>

using namespace std;

string concat(string str, const string& strAdd) {
    if (!strAdd.empty() && strAdd != "Zero") {
        str += " ";
        str += strAdd;
    }
    return str;
}

string numberToWords(int num) {
    static const vector<string> ones {"","One","Two","Three","Four","Five","Six","Seven","Eight","Nine"};
    static const vector<string> teens {"Ten","Eleven","Twelve","Thirteen","Fourteen","Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"};
    
    if (num < 0) return "";
    if (num == 0) return "Zero";
    if (num<10) return ones[num];
    if (num<20) return teens[num-10];
    if (num<30) return concat("Twenty",ones[num-20]);
    if (num<40) return concat("Thirty",ones[num-30]);
    if (num<50) return concat("Forty",ones[num-40]);
    if (num<60) return concat("Fifty",ones[num-50]);
    if (num<70) return concat("Sixty",ones[num-60]);
    if (num<80) return concat("Seventy",ones[num-70]);
    if (num<90) return concat("Eighty",ones[num-80]);
    if (num<100) return concat("Ninety",ones[num-90]);
    if (num<1000) return ones[num/100]+concat(" Hundred", numberToWords(num-(num/100)*100));
    if (num<1000000) return numberToWords(num/1000)+concat(" Thousand",numberToWords(num-(num/1000)*1000));
    if (num<1000000000) return numberToWords(num/1000000)+concat(" Million",numberToWords(num-(num/1000000)*1000000));
    return numberToWords(num/1000000000)+concat(" Billion",numberToWords(num-(num/1000000000)*1000000000));
}

int main() {
    cout << numberToWords(1234567891) << "\n";
    return 0;
}