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)".

public class Solution {
    public String fractionToDecimal(int numerator, int denominator) {
        // http://blog.csdn.net/ljiabin/article/details/42025037
        if (numerator == 0)
            return "0";
            
        if (denominator == 0)
            return "";  
          
        String ans = "";  
          
        // If different signs 
        if ((numerator < 0) ^ (denominator < 0))
            ans += "-";
          
        // Converto to 'long' type in case of overflow 
        long num = Math.abs((long)numerator);  
        long den = Math.abs((long)denominator);  
          
        // Get integer quotient
        long res = num/den;
        ans += String.valueOf(res);  

        // (Remainder*10) / denominator in case of integer division
        long rem = (num % den) * 10;
        
        // Check if there is remainder
        if (rem == 0)
            return ans;  
          
        // Fractional part --- <Remainder, Index>  
        HashMap<Long, Integer> map = new HashMap<>();
        
        ans += ".";  
        
        while (rem != 0)
        {  
            // If this remainder has already appeared, it indicates loop.
            if (map.containsKey(rem))
            {
                // Obtain index of loop remainder
                int id = map.get(rem);
                
                String nonLoop = ans.substring(0, id);  
                String loop = ans.substring(id, ans.length());
                
                ans = nonLoop + "(" + loop + ")";  
                return ans;  
            }  
              
            // Continue division 
            map.put(rem, ans.length());
            
            res = rem / den;  
            ans += String.valueOf(res);  
            rem = (rem % den) * 10;  
        }  
          
        return ans;        
    }
}