string to integer / atoi

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"""
https://leetcode.com/problems/string-to-integer-atoi/description/
"""


class Solution(object):
    def myAtoi(self, st):
        """
        :type str: str
        :rtype: int
        >>> s = Solution()
        >>> s.myAtoi("42")
        42
        >>> s.myAtoi("   -42")
        -42
        >>> s.myAtoi("4193 with words")
        4193
        >>> s.myAtoi("words and 987")
        0
        >>> s.myAtoi("-91283472332")
        -2147483648
        >>> s.myAtoi("  -12-45")
        -12
        >>> s.myAtoi("-")
        0
        >>> s.myAtoi("- 1")
        0
        >>> s.myAtoi("- 1")
        0
        >>> s.myAtoi("- -1")
        0
        >>> s.myAtoi("+1")
        1
        >>> s.myAtoi("123  456")
        123
        """
        INT_MAX = 2**31 - 1
        INT_MIN = -2**31
        start, end = -1, -1
        if st == "":
            return 0
        for idx, i in enumerate(st):
            if i == " ":
                if start != -1:
                    end = idx
                    break
            elif i in set({"-", "+"}):
                if start == -1:
                    start = idx
                else:
                    end = idx
                    break

            elif i in set({"0", "1", "2", "3", "4", "5", "6", "7", "8", "9"}):
                if start == -1:
                    start = idx
            else:
                if start == -1:
                    return 0
                else:
                    end = idx
                    break
        try:
            if end == -1:
                value = int(st[start:])
            else:
                value = int(st[start:end])
        except ValueError:
            return 0
        if value > INT_MAX:
            return INT_MAX
        if value < INT_MIN:
            return INT_MIN
        return value

    def myAtoi2(self, st):
        """
        :type str: str
        :rtype: int
        """
        import re
        st = st.strip()
        try:
            res = re.search('(^[\+\-]?\d+)', st).group()
            res = int(res)
            res = res if res <= 2147483647 else 2147483647
            res = res if res >= -2147483648 else -2147483648
        except:
            res = 0
        return res