273.cpp

//
//  273.cpp
//  leetcode
//
//  Created by R Z on 2018/7/22.
//  Copyright © 2018年 R Z. All rights reserved.
//

#include <stdio.h>
#include <string>
using namespace std;
class Solution {
public:
    static string numberToWords(int n) {
        if(n == 0) return "Zero";
        else return int_string(n).substr(1);
    }
private:
    static const char * const below_20[];
    static const char * const below_100[];
    static string int_string(int n) {
        if(n >= 1000000000)   return int_string(n / 1000000000) + " Billion" + int_string(n - 1000000000 * (n / 1000000000));
        else if(n >= 1000000) return int_string(n / 1000000) + " Million" + int_string(n - 1000000 * (n / 1000000));
        else if(n >= 1000)    return int_string(n / 1000) + " Thousand" + int_string(n - 1000 * (n / 1000));
        else if(n >= 100)     return int_string(n / 100) + " Hundred" + int_string(n - 100 * (n / 100));
        else if(n >= 20)      return string(" ") + below_100[n / 10 - 2] + int_string(n - 10 * (n / 10));
        else if(n >= 1)       return string(" ") + below_20[n - 1];
        else return "";
        
    }
};

const char * const Solution::below_20[] =  {"One", "Two", "Three", "Four","Five","Six","Seven","Eight","Nine","Ten", "Eleven","Twelve","Thirteen","Fourteen","Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"};
const char * const Solution::below_100[] = {"Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};