8.string-to-integer-atoi.python3.py

#
# [8] String to Integer (atoi)
#
# https://leetcode.com/problems/string-to-integer-atoi/description/
#
# algorithms
# Medium (14.14%)
# Total Accepted:    270K
# Total Submissions: 1.9M
# Testcase Example:  '"42"'
#
# 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.
# 
#
class Solution:
    def myAtoi(self, str):
        """
        :type str: str
        :rtype: int
        """
        string = str.strip()
        if not string:
            return 0
        elif string[0] not in '+-' and not self.is_num(string[0]):
            return 0
        elif string in '+-': 
            return 0
        elif string[0] in '+-' and not self.is_num(string[1]):
            return 0

        flag = True
        for i in range(1, len(string)):
            if not self.is_num(string[i]):
                flag = False
                break

        if flag:
            convert_string = string
        else:
            convert_string = string[:i]

        res = int(convert_string)
        if res > 2 ** 31 - 1:
            return 2 ** 31 - 1
        elif res < -(2 ** 31):
            return -2 ** 31
        else:
            return res

    def is_num(self, char):
        ord_val = ord(char)
        if ord_val > 47 and ord_val < 58:
            return True
        else:
            return False


# if __name__ == "__main__":
#     string = '43'
#     ex = Solution()
#     print(ex.myAtoi(string))