public class Solution { public String fractionToDecimal(int numerator, int denominator) { StringBuffer sb = new StringBuffer(); if((numerator > 0 && denominator <0) || (numerator < 0 && denominator >0))sb.append("-"); long num = Math.abs((long)numerator); long den = Math.abs((long)denominator); sb.append(num/den); if(num%den == 0) return sb.toString(); sb.append("."); // dont forget!!! num %= den; HashMap map = new HashMap(); map.put(num, sb.length()); while(num!=0){ num*=10; //dont forget!!! sb.append(num/den); num%=den; if(map.containsKey(num)){ int index = map.get(num); sb.insert(index, "("); sb.append(")"); return sb.toString(); } else{ map.put(num, sb.length()); } } return sb.toString(); } }