String to Integer (atoi)

Description:

Implement function atoi to convert a string to an integer.

If no valid conversion could be performed, a zero value is returned.

If the correct value is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648) is returned.

Example “10” => 10 “-1” => -1 “123123123123123” => 2147483647 “1.0” => 1

Code:

class Solution:
    """
    @param str: A string
    @return: An integer
    """
    def atoi(self, str):
        # write your code here
        if not str:
            return 0
        res = 0
        st = 0
        sign = 1
        for i in range(len(str)):
            if str[i]!=' ':
                str
 
 = str[i:]
                break
        
        if str[0]=='+':
            st += 1
        elif str[0]=='-':
            st += 1
            sign = -1

        for i in range(st, len(str)):
            if str[i]<'0' or str[i]>'9':
                break
            else:
                res *= 10
 

                res += int(str[i])
        res *= sign
        if res>2147483647:
            return 2147483647
        if res<-2147483648:
            return -2147483648
        return res