273. Integer to English Words

Task:

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"

Some Questions:

How to spell 1 to 19?

How to spell 20,30,40,...,90?

Solution:

According to the grammar, it reads integer three digits by three digits. So we can convert the Integer into English three digits by three digits.

Thus we need to implement a helper to convert a number within 1000. At last, For every group of three digits, add the suffix of weight to it.

Attention to corner cases!

Code:

class Solution {    const string Mil="Million";    const string Tho="Thousand";    const string Bil="Billion";    const string Hun="Hundred";    string tab[20]={"Zero","One","Two","Three","Four","Five","Six","Seven","Eight","Nine","Ten","Eleven","Twelve","Thirteen","Fourteen","Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"};    string tens[10]={"Zero","Ten","Twenty","Thirty","Forty","Fifty","Sixty","Seventy","Eighty","Ninety"};    string calc(int n,int w)    {        if(n==0)return "";        string ret="";        if(n>=100)        {            if(ret!="")ret+=" ";            ret+=tab[n/100]+" "+Hun;        }        n%=100;        if(n>0)        {            if(n<20)            {                if(ret!="")ret+=" ";                ret+=tab[n];            }            else            {                if(ret!="")ret+=" ";                if(n%10!=0)                {                    ret+=tens[n/10]+" "+tab[n%10];                }                else ret+=tens[n/10];            }        }                if(w==1)        {            ret+=" "+Tho;        }        else if(w==2)        {            ret+=" "+Mil;        }        else if(w==3)        {            ret+=" "+Bil;        }        return ret;    }public:    string numberToWords(long long num) {        int bit[4];        string ret="";        int len=0;        if(num==0)return "Zero";        while(num)        {            bit[len++]=num%1000;            num/=1000;        }        int i;        for(i=len-1;i>=0;i--)        {            string tmp=calc(bit[i],i);            if(tmp!="")            {                if(ret!="")ret+=" ";                ret+=tmp;            }        }        return ret;    }};