[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)".

 

两个问题：

1.如何找到循环小时部分，解决方法是Hash table，存储已经出现过的余数，当他再次出现说明开始循环了。这和Happy Number解法一样，Hash table判断是否有循环出现。

2.INT的最大值和最小值，比如INT_MIN=-2147483648，取绝对值后就超过了INT_MAX=2147483647了，解决方法是使用long long类型。

class Solution {
public:
    string fractionToDecimal(int  numerator, int  denominator) {
        string result;
        long long num=numerator,den=denominator;
        if(numerator==0)
        {
            return "0";
        }
        if((numerator<0)^(denominator<0))
        {
            result+='-';
        }
        if(numerator<0)
        {
            num=-1*num;
        }
        if(denominator<0)
        {
            den=-1*den;
        }
        long long int_part=num/den;
        result+=to_string(int_part);
        if(num%den==0)
        {
            return result;
        }
        result+='.';
        long long left=num%den;
        unordered_map<long long,int> showed;
        while(left)
        {
            if(showed.find(left)!=showed.end())
            {
                int position=showed[left];
                string part1=result.substr(0,position);
                string part2=result.substr(position,result.length());
                result = part1+'('+part2+')';
                return result;
            }
            showed[left]=result.length();
            left*=10;
            int dig=left/den;
            result+=to_string((long long)dig);
            left = left%den;
        }
        return result;
    }
};