leetcode -- Fraction to Recurring Decimal -- 数学题，知道相除规则

https://leetcode.com/problems/fraction-to-recurring-decimal/

参考
http://yucoding.blogspot.hk/2015/03/leetcode-question-fraction-to-recurring.html
的计算方法。思路见code

class Solution:
    # @return a string
    def fractionToDecimal(self, numerator, denominator):
        if numerator * denominator < 0:
            pos = False
        else:
            pos = True
        numerator = abs(numerator)
        denominator = abs(denominator)

        maxlen=1000#最多求到小数点后1000位
        mod = []#reminder的集合
        if numerator == 0 or denominator == 0:
            return "0"
        res = []#quotient的集合，也是结果的集合
        l = -1
        while len(mod) < maxlen:#一直除到小数位数超过给定的maxlen
            res.append(numerator/denominator)
            m = numerator % denominator
            if m == 0:
                break
            if m in mod:
                l = mod.index(m)#如果reminder在以前出现过，那么后面的结果就是在这个reminder对应的index开始不断的重复。重复res[l::]的结果，所以对这一部分加上括号就可以了
                break
            else:
                mod.append(m)
                numerator = m * 10

        if len(res) == 1:#可以被整除，e.g. 6/3 = 2
            s = str(res[0])
        else:#结果是小数
            s = str(res[0]) + "."
            if l == -1:#结果是不循环小数
                s = s + "".join([str(n) for n in res[1::]] )
            else:#结果是循环小数
                s = s+ "".join([str(n) for n in res[1:l+1]]) + "(" + "".join([str(n) for n in res[l+1::]]) + ")"
        if pos:
            return s
        else:
            return "-"+s

自己重写code

class Solution(object):
    def fractionToDecimal(self, numerator, denominator):
        """ :type numerator: int :type denominator: int :rtype: str """
        sign = 1
        if numerator * denominator < 0:
            sign = -1
        numerator, denominator = abs(numerator), abs(denominator)
        if numerator == 0 or denominator == 0: return '0'#这个注意加上

        if numerator % denominator == 0 : return  str(sign *numerator/denominator)


        res = []
        mod = []

        res_index = -1
        while len(mod) < 1000:

            res1 = numerator / denominator
            mod1 = numerator % denominator

            if mod1 == 0:
                res.append(str(res1))#这个要记得加上， 或者直接在计算res1的时候就res.append
                break
            elif mod1 in mod:
                res_index = mod.index(mod1)
                res.append(str(res1))#这个要记得加上， 或者直接在计算res1的时候就res.append
                break

            res.append(str(res1))
            mod.append(mod1)
            numerator = mod1 * 10

        if res_index == -1:
            if sign == -1:
                return '-' + str(res[0]) + '.' +''.join(res[1:])
            return str(res[0]) + '.' +''.join(res[1:])
        else:
            if sign == -1:
                return '-' + str(res[0]) + '.' + ''.join(res[1:res_index + 1]) + '(' + ''.join(res[res_index + 1:]) + ')'
            return str(res[0]) + '.' + ''.join(res[1:res_index + 1]) + '(' + ''.join(res[res_index + 1:]) + ')'