29. Divide Two Integers 按位做循环减法，

运用一般的循环减法，会超时。
运用按位左移的方法，实在是妙！值得细细体会

class Solution:
    
    def divide(self, dividend: int, divisor: int) -> int:
        if divisor == 0 or dividend == 0:
            return 0
        if (dividend < 0 and divisor < 0) or (dividend > 0 and divisor > 0):
            flag = True
        else:
            flag = False
        
        if dividend == -2147483648 and divisor == -1:
            return 2147483647
        if divisor == 1:
            return dividend
        
        dividend = abs(dividend)
        divisor = abs(divisor)
        count = 0
        for i in reversed(range(31)):
            cur = divisor << i
            if dividend >= cur:
                count |= 1 << i
                dividend = dividend - cur
                # print(i, dividend, divisor)
        if not flag:
            count = 0 - count
        return count