题解 | #学英语#

#include<bits/stdc++.h>
using namespace std;
string ones[] = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };
string tens[] = { "ten","eleven","twelve","thirteen","fourteen","fifteen","sixteen","seventeen","eighteen","nineteen" };
string twenties[] = { "zero","ten","twenty","thirty","forty","fifty","sixty","seventy","eighty","ninety" };
string hundreds[] = { "hundred", "thousand", "million", "billion" };
int ihundreds[] = { (int)1e2, (int)1e3, (int)1e6, (int)1e9, (int)1e12 };
string itoe(long long n)
{
    if (n<=9)return ones[n];
    else if (n<20)return tens[n%10];
    else if (n<1e2)return twenties[n/10] + (n%10 ? " " + ones[n%10] : "");
    else for (int i=0; i < 4; i++)
        if (n < ihundreds[i+1])
            return itoe(n/ihundreds[i]) + " " 
            + hundreds[i] 
            + (n%ihundreds[i] ? (i ? " ": " and ") + itoe(n%ihundreds[i]) : "");
    return "";
}
int main()
{
    long long n;
    while (cin>>n)
        cout<<itoe(n)<<endl;
}