【Leetcode 166】 Fraction to Recurring Decimal

Description:

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)".

Solution:

　　long division: 长除法

　　Trick： Determining whether two nums have different sign(+ or  -) can use follow codes:

if((n<0)^(d<0))  //异号
or
if((n>0)^(d>0))  //异号

　　Above code avoiding product's value overflow.

Code:

class Solution {
public:
    string fractionToDecimal(int numerator, int denominator) {
        if(!numerator) return "0";
        long long n = numerator, d = denominator;
        string ret = "";
        if((n<0)^(d<0)) ret += '-';
        if(n < 0) n = -n;
        if(d < 0) d = -d;
        ret += to_string(n/d);
        if(n % d == 0){
            return ret;
        }ret += '.';
        map<long long, int>hash;
        for(long long r = n % d; r; r %= d){
            if(hash.find(r) != hash.end()){
                ret.insert(hash[r],"(");
                ret += ")";
                return ret;
            }
            hash[r] = ret.size();
            r *= 10;
            ret += to_string(r / d);
        }
    }
};