Python3 代码

class Solution(object):
    def strToInt(self, str):
        """
        :type str: str
        :rtype: int
        """
        MAX_INT = 2147483647
        MIN_INT = -2147483648 

        num = 0
        sign = 1

        k = 0

        # trim
        while k < len(str) and str[k] == " ":
            k += 1

        # read sign 
        for i in range (k, len(str)):
            if str[i] == "-":
                sign = -1 
                continue 
            if str[i] == "+":
                continue
            if str[i] < "0" or str[i] > "9":
                break

            num = num * 10 + int(str[i])

        num *= sign

        if num > MAX_INT:
            return MAX_INT
        if num < MIN_INT:
            return MIN_INT

        return num