[leedcode 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) {
          //注意正负
          //注意越界（转为long）
          //使用map记录余数和位置，当发现相同的余数时，则表示此余数对应位置的商位开始循环，此时需要用()包装
          //seq表示商
          long num=Math.abs((long)numerator);
          long deno=Math.abs((long)denominator);
          int flag=1;
          if(numerator>0&&denominator<0||numerator<0&&denominator>0) flag=0;
          long s=num/deno;
          long t=num%deno;
          String res=flag==0?"-"+Long.toString(s):Long.toString(s);
          if(t==0) return res;
          else return res+"."+getRes(t,deno);
  
      }
      public StringBuilder getRes(long t,long deno){
          StringBuilder seq=new StringBuilder();
          HashMap<Long,Integer> map=new HashMap<Long,Integer>();
          int i=0;
          while(t!=0&&!map.containsKey(t)){
              map.put(t,i);
              i++;
              t*=10;
              seq.append(Long.toString(t/deno));
              t%=deno;
  
          }
          if(t!=0){
              seq.insert((int)map.get(t),‘(‘);
              seq.append(‘)‘);
          }
          return seq;
      }
  }