leetcode166. Fraction to Recurring Decimal

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本文介绍了一种将分数转换为小数格式的算法，并详细解释了如何处理循环小数的情况。通过使用字典记录余数及其对应位置，该算法能够准确地识别循环节并将其括入括号内。

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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)”.
Credits:
Special thanks to @Shangrila for adding this problem and creating all test cases.

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思路
几个注意点：
正负号问题，numerator=0问题
解法是使用两个字典，一个字典key=余数，value=下一个相除结果
另外一个字典key=余数，value=当前的位置，同时计算时用一个列表将结果一一加入
余数==0或者余数已经在字典1中出现，则当前位置以前的序列是括号外面的字符串，当前位置以后是括号里面的字符串
注意一些细节，比如temp要重新赋值等等～～

class Solution(object):
    def fractionToDecimal(self,numerator,denominator):
        if (numerator>=0 and denominator>0) or (numerator<=0 and denominator<0):
            flag=1
        else:
            flag=0
        numerator=abs(numerator)
        denominator=abs(denominator)
        intenger=numerator/denominator
        remainder=numerator%denominator
        if remainder==0:
            if not flag:
                ss='-'+str(intenger)
            else:
                ss=str(intenger)
            return ss
        doc={}
        ans=[]
        id1={}
        i=0
        while remainder!=0 and remainder not in doc:
            temp=remainder*10/denominator
            doc.setdefault(remainder,temp)
            id1.setdefault(remainder,i)
            i=i+1
            ans.append(str(temp))
            remainder=remainder*10%denominator
        temp=remainder*10/denominator
        if  remainder:
            t1="".join([ans[i] for i in range(id1[remainder])])
            t2="".join([ans[i] for i in range(id1[remainder],len(ans))])
            if t1:
                s=str(intenger)+'.'+t1+'('+t2+')'
            else:
                s=str(intenger)+'.('+t2+')' 
        else:
            ss="".join([ans[i] for i in range(len(ans))])
            s=str(intenger)+'.'+ss
        if not flag:
            s='-'+s
        return s