【python3】leetcode 8. String to Integer (atoi) （Meidum）

8. String to Integer (atoi) （Meidum） 

Given two integers dividend and divisor, divide two integers without using multiplication, division and mod operator.

Return the quotient after dividing dividend by divisor.

The integer division should truncate toward zero.

Example 1:

Input: dividend = 10, divisor = 3
Output: 3

Example 2:

Input: dividend = 7, divisor = -3
Output: -2

Note:

• Both dividend and divisor will be 32-bit signed integers.
• The divisor will never be 0.
• Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231,  231 − 1]. For the purpose of this problem, assume that your function returns 231 − 1 when the division result overflows.

class Solution:
    def myAtoi(self, str):
        """
        :type str: str
        :rtype: int
        """
        import builtins
        s = str

        INT_MAX = (1<<31) - 1
        INT_MIN = -1 * 1<<31
        _digits = [builtins.str(x) for x in range(0,10)]
        s = s.strip()
        if len(s) == 0:return 0
        #while(s[0] == ' '):s = s[1:]
        sumx = 0
        if s[0] not in ['+','-'] + _digits:
            return 0
        tag = -1 if s[0] == '-' else 1
        if s[0] in ['+','-']:s = s[1:]
        for i in s:
            if i in _digits:
                sumx = sumx*10 + int(i)
            else:break
        if  tag * sumx< INT_MIN :return INT_MIN 
        elif tag * sumx > INT_MAX :return INT_MAX 
        return tag * sumx