leetcode8

# # -*- coding:utf-8 -*-
#
#
# # Implement atoi which converts a string to an integer.
# #
# # 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.
# #
# # Note:
# #
# #
# # 	Only the space character ' ' is considered as whitespace character.
# # 	Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231,  231 − 1].
# If the numerical value is out of the range of representable values, INT_MAX (231 − 1) or
# INT_MIN (−231) is returned.
# #
# #
# # Example 1:
# #
# #
# # Input: "42"
# # Output: 42
# #
# #
# # Example 2:
# #
# #
# # Input: "   -42"
# # Output: -42
# # Explanation: The first non-whitespace character is '-', which is the minus sign.
# #              Then take as many numerical digits as possible, which gets 42.
# #
# #
# # Example 3:
# #
# #
# # Input: "4193 with words"
# # Output: 4193
# # Explanation: Conversion stops at digit '3' as the next character is not a numerical digit.
# #
# #
# # Example 4:
# #
# #
# # Input: "words and 987"
# # Output: 0
# # Explanation: The first non-whitespace character is 'w', which is not a numerical
# #              digit or a +/- sign. Therefore no valid conversion could be performed.
# #
# # Example 5:
# #
# #
# # Input: "-91283472332"
# # Output: -2147483648
# # Explanation: The number "-91283472332" is out of the range of a 32-bit signed integer.
# #              Thefore INT_MIN (−231) is returned.
# #
import re
def atoi(strs):
    strs=re.sub("^ +","",strs)
    if strs[0]=='-':
        neg='-'
    else:
        neg=''
    strs = strs.replace("-", "").replace("+", "")
    if re.findall("^\d+",strs)==[]:
        return 0
    else:
        id=int(neg+re.findall("^\d+",strs)[0])
        if id>2**31-1:
            return 2**31-1
        elif  id<-2**31:
            return -2**31
        else:
            return id
print(atoi("4193 with words"))