Fraction to Recurring Decimal——数值处理&&哈希表

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)".

Hint:

No scary math, just apply elementary math knowledge. Still remember how to perform a long division?

 

这题就是按定义做。

如果不能整除,就不断进行余数补零除以除数。

维护一个映射表map<long long, int> m, 用来记录每个余数对应返回值ret中的位置。

(1)当出现重复的余数r时,说明找到了循环体,根据m[r]找到ret中位置,加上相应的'('和')'将循环体括起来即可返回。

(2)当余数r为0时,返回ret。

注意点:可能出现INT_MIN/-1的越界情况,因此第一步现将int转为long long int

class Solution {
public:
    string fractionToDecimal(int numerator, int denominator) {
        if(denominator==0)
            return "";
        if(numerator==0)
            return "0";
        string res;
        long long num=numerator;
        long long den=denominator;
        if((num<0)^(den<0))
        {
            res+="-";
            num=abs(num);
            den=abs(den);
        }
        long long temp=num/den;
        res+=to_string(temp);
        if (num%den==0)
            return res;
        res+=".";
        temp=num%den;
        map<long long,int> m;
        while(temp!=0)
        {
            if(m.find(temp)!=m.end())
            {
                res.insert(m[temp], 1, '(');   //insert (iterator p, size_t n, char c);
                res += ')';
                return res;    
            }
            m[temp] = res.size();
            temp*=10;
            res+=to_string(temp/den);
            temp%=den;
        }
        return res;
    }
};

 

posted @ 2015-06-11 14:59  linqiaozhou  阅读(273)  评论(0)    收藏  举报