string-to-integer-atoi.py

# -*- coding:utf-8 -*-


# Implement atoi to convert a string to an integer.
#
# Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.
#
#
# Notes: 
# It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front. 
#
#
# Update (2015-02-10):
# The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button  to reset your code definition.
#
#
# spoilers alert... click to show requirements for atoi.
#
# Requirements for atoi:
#
# The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes an optional initial plus or minus sign followed by as many numerical digits as possible, and interprets them as a numerical value.
#
# The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.
#
# If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed.
#
# 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.


class Solution(object):
    def myAtoi(self, str):
        """
        :type str: str
        :rtype: int
        """
        import re
        p = re.compile(r'^[+-]?[0-9]+')
        m = re.match(p, str.strip())
        if m:
            ret = int(m.group())
            if ret < -0x80000000:
                return -0x80000000
            elif ret > 0x7fffffff:
                return 0x7fffffff
            return ret
        else:
            return 0