leetcode 166. 分数到小数

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题目链接：leetcode

思路：

  • 不存在循环小数
  • 存在循环小数，形如1.2(3456)
  • 存在循环小数，形如1.(3456)
  • 使用字典存储余数mod，每次循环更新余数，如果字典中存在，说明循环了，再构造字符串
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class Solution(object):
    def fractionToDecimal(self, numerator, denominator):
        """
        :type numerator: int
        :type denominator: int
        :rtype: str
        """
        prefix = '-' if numerator*denominator < 0 else ''
        numerator = abs(numerator)
        denominator = abs(denominator)
        divide = numerator//denominator
        mod = numerator%denominator
        if mod == 0:return prefix+str(divide)
        d = {}
        stack = []
        i = -1
        while True:
            if mod == 0:
                return prefix+str(divide)+'.'+''.join(stack)
            mod *= 10
            i += 1
            if mod in d:
                idx = d[mod]
                return prefix+str(divide)+'.'+''.join(stack[:idx])+'('+''.join(stack[idx:])+')'
            
            if mod < denominator:
                stack.append('0')
                d[mod] = i
            else:
                stack.append(str(mod//denominator))
                d[mod] = i
                mod = mod%denominator