0166：分数到小数（★）

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19

class Solution:
    def fractionToDecimal(self, numerator: int, denominator: int) -> str:
        res = '' if numerator*denominator>=0 else '-'
        x,y = abs(numerator),abs(denominator)
        q,r = divmod(x,y)
        res += str(q)
        if r==0:
            return res
        res += '.'
        d = {r:len(res)}
        while True:
            q,r = divmod(r*10,y)
            res += str(q)
            if r==0:
                return res
            if r in d:
                j = d[r]
                return res[:j]+'('+res[j:]+')'
            d[r] = len(res)