29. 兩數相除（中等）（1.5）

給定兩個整數，被除數 dividend 和除數 divisor。將兩數相除，要求不使用乘法、除法和 mod 運算符。

返回被除數 dividend 除以除數 divisor 得到的商。

示例 1:

輸入: dividend = 10, divisor = 3
輸出: 3

class Solution(object):
    def divide(self, dividend, divisor):
        """
        :type dividend: int
        :type divisor: int
        :rtype: int
        """
        result=0
        divi=abs(dividend)
        div=abs(divisor)
        while divi>=div:
            divi-=div
            result+=1
        if dividend*divisor>0:
            return result
        else:
            return -result
        

超出時間了

class Solution(object):
    def negative(self, n):
        return ~n+1
    def positive(self, n):
        t = n >> 31
        return (n + t) ^ t
    def negpos(self, sign, n):
        return self.positive(n) if sign else self.negative(n)
    def divide(self, dividend, divisor):        
        sign = dividend >> 31 == divisor >> 31
        dividend = self.positive(dividend)
        divisor = self.positive(divisor)
        cnt, minus = 0, divisor
        while dividend >= minus:
            minus <<= 1
            cnt += 1
        if cnt == 0:
            return 0
        r = self.negpos(sign, 2**(cnt-1) +
                        self.divide(dividend-(minus >> 1), divisor))
        if r < -2**31 or r > 2**31 - 1:
            return 2**31 - 1
        return r
        

執行用時: 36 ms, 在Divide Two Integers的Python提交中擊敗了91.82% 的用戶