Leetcode-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)".

Analysis:

We need to use long type.

Solution:

Store every digit in float part, and assemble the string at last.

public class Solution {
    public String fractionToDecimal(int numerator, int denominator) {
        if (denominator==0) return "";
        if (numerator==0) return "0";
        boolean neg = false;
        if (numerator>0){
            numerator = -numerator;
            neg = !neg;
        }

        if (denominator>0){
            denominator = -denominator;
            neg = !neg;
        }
 

        long intPart = (long) numerator/ (long) denominator;
        long left = numerator%denominator;

        List<Integer> digitList = new ArrayList<Integer>();
        List<Long> leftList = new ArrayList<Long>();
        int iterStart = -1;
        while (left!=0){
            int digit = (int) (left*10/denominator);
            digitList.add(digit);
            leftList.add(left);
            long newLeft = (left*10)%denominator;
            if (leftList.contains(newLeft)){
                iterStart = leftList.indexOf(newLeft);
                break;
            }
            left = newLeft;
        }

        //Assemble the string.
        StringBuilder builder = new StringBuilder();
        if (neg) builder.append('-');
        builder.append(intPart);

        if (digitList.size()==0) return builder.toString();
        else {
            builder.append('.');
            if (iterStart==-1)
                for (int i=0;i<digitList.size();i++)
                    builder.append(digitList.get(i));
            else {
                //append non-iter part.
                for (int i=0;i<iterStart;i++)
                    builder.append(digitList.get(i));
                builder.append('(');
                //append iter part.
                for (int i=iterStart;i<digitList.size();i++)
                    builder.append(digitList.get(i));
                builder.append(')');
            }
            return builder.toString();
       }        
        
    }
}

Solution 2:

Store the postion of the corresponding left of every digit, assemble the result string in place.

public class Solution {
    public String fractionToDecimal(long numerator, long denominator) {
        if (denominator==0) return "";
        if (numerator==0) return "0";
        String res = "";
        if (numerator<0 ^ denominator<0)
            res = "-";         
 
        numerator = Math.abs(numerator);
        denominator = Math.abs(denominator);

        long intPart = numerator/denominator;
        long left = numerator%denominator;
        res = res.concat(Long.toString(intPart));
        Map<Long,Integer> posMap = new HashMap<Long,Integer>();
        if (left!=0) res = res.concat(".");
        while (left!=0){
            long digit = left*10/denominator;
            posMap.put(left,res.length());
            res = res.concat(Long.toString(digit));
            left = left*10%denominator;
            if (posMap.containsKey(left)){
                int pos = posMap.get(left);
                res = res.substring(0,pos)+"("+res.substring(pos,res.length())+")";
                left = 0;
            }
        }            

        return res;        
        
    }
}