leetcode[166]Fraction to Recurring Decimal

Given two integers representing the numerator and denominator of a fraction, return the fraction in string format.

If the fractional part is repeating, enclose the repeating part in parentheses.

For example,

     Given numerator = 1, denominator = 2, return "0.5".

     Given numerator = 2, denominator = 1, return "2".

     Given numerator = 2, denominator = 3, return "0.(6)".

class Solution {

public:

string  to_str(long long  n)

{

    string str="";

    if(n==0)

    {

        str+='0';

        return str;

    }

    long long tmp=n;

    long long power=1;

    int icount=0;

    while (tmp)

    {

        tmp/=10;

        power*=10;

        icount++;

    }

    power/=10;

    tmp=n;

    for (int i=0;i<icount;i++)

    {

        long long d=tmp/power;

        str+=char('0'+d);

        tmp-=d*power;

        power/=10;

    }

    return str;

}

string fractionToDecimal(int numerator, int denominator) {

    if(denominator==0)return "";

    if(numerator==0)return "0";

    string res="";

    long long num=numerator,  den=denominator;

    if((num>0&&den<0)||(num<0&&den>0))

        res+="-";

    num=num>=0?num:-num,den=den>=0?den:-den;

    long long part=num/den;

    res+=to_str(part);

    long long f=num%den;

    if(f==0)return res;

    res+='.';

    map<int,int> fmap;

    while(f)

    {

        if (fmap.count(f))

        {

            int beg=fmap[f];

            string part1=res.substr(0,beg);

            string part2=res.substr(beg,res.length());

            res=part1+"("+part2+")";

            return res;

        } 

        else

        {

            fmap[f]=res.length();            

            f*=10;

            res+=to_str(f/den);

            f%=den;        

        }

    }

    return res;

}

};