【leetcode】Fraction to Recurring Decimal

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)".

    0.16
6 ) 1.00
    0
    1 0       <-- Remainder=1, mark 1 as seen at position=0.
    - 6
      40      <-- Remainder=4, mark 4 as seen at position=1.
    - 36
       4      <-- Remainder=4 was seen before at position=1, so the fractional part which is 16 starts repeating at position=1 => 1(6).

如果发现余数曾经出现过，则说明开始循环了，利用一个hash表记录余数出现的位置即可

注意INT_MIN转换成正数会溢出，故需要先把数字先转为long long int

注意余数也要去long long int，因为-1,2147483648这种情况下，余数在计算乘以10的过程中会溢出

 

 class Solution {
 public:
     string fractionToDecimal(int numerator, int denominator) {

         string ans="";
         if(numerator==) return "";

         long long int n=numerator;
         long long int d=denominator;
         n=abs(n);
         d=abs(d);

         if(numerator<^denominator<) ans.push_back('-');

         map<long long int,int> hash;

         ans+=to_string(n/d);
         long long int rem=n%d;
         if(rem!=) ans.push_back('.');

         while(rem!=)
         {
             if(hash.find(rem)!=hash.end())
             {
                 ans.insert(hash[rem],"(");
                 ans.push_back(')');
                 break;
             }

             hash[rem]=ans.length();

             ans+=to_string(rem*/d);
             rem=(rem*)%d;
         }

         return ans;
     }
 };