【leetcode刷题】29. Divide Two Integers

原题链接
https://leetcode.com/problems/divide-two-integers/
解题思路
除法的本质是减法，但是如果此题采用被除数不断减去除数的方法，对于被除数很大而除数很小的情况，会产生RunTimeError；因此考虑移位算法，使除数以的指数倍增长，提高计算效率。除此以外还需要注意两点：一是符号的判断，二是溢出。
代码

class Solution(object):
    def divide(self, dividend, divisor):
        """
        :type dividend: int
        :type divisor: int
        :rtype: int
        """
        # sign flag
        isPos = True
        if (dividend >= 0 and divisor < 0) or (dividend <= 0 and divisor > 0):
            isPos = False
        dividend = abs(dividend)
        divisor = abs(divisor)

        if dividend < divisor:
            return 0

        ans = 0
        while dividend - divisor >= 0:
            result, dividend = self.increaseAnswer(dividend, divisor)
            ans += result
        if isPos == False:
            if ans < -2147483648:
                return -2147483648
            return -ans
        elif ans > 2147483647:
            return 2147483647
        return ans

    def increaseAnswer(self, dividend, divisor):
        result = 1
        while dividend - divisor >= 0:
            result <<= 1
            divisor <<= 1
        result >>= 1
        divisor >>=1
        return result, dividend-divisor

参考：https://www.cnblogs.com/zuoyuan/p/3779359.html