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.

Source: leetcode | Difficulty: MEDIUM_HARD
Tags: String algorithms

Starter code: class Solution:
    def myAtoi(self, s: str) -> int:
        

Solutions:
class Solution:

	def myAtoi(self, str):
		base = '0123456789'
		plus = '+'
		minus = '-'
		sum = 0
		flag = 1
		bit = 0
		INT_MAX = 2147483647
		INT_MIN = -2147483648
		if not str:
			return 0
		if len(str) == 0:
			return 0
		for letter in str.strip():
			if letter in plus:
				if bit == 0:
					bit = 1
					continue
				else:
					break
			elif letter in minus:
				if bit == 0:
					bit = 1
					flag = -1
					continue
				else:
					break
			elif letter not in base:
				break
			else:
				sum *= 10
				sum += int(letter)
		sum *= flag
		if sum > INT_MAX:
			return INT_MAX
		if sum < INT_MIN:
			return INT_MIN
		return sum


class Solution:

	def myAtoi(self, str):
		import sys
		str = str.lstrip()
		if not str:
			return 0
		negative = str[0] == '-'
		str = str.lstrip('')
		if str[0] in ('-', '+'):
			str = str[1:]
		str.lstrip('0')
		result = 0
		for s in str:
			if s.isnumeric():
				result *= 10
				result += int(s)
			else:
				break
		return max(min(result * (-1 if negative else 1), 2147483647), -2147483648)


class Solution:

	def myAtoi(self, str):
		str = str.strip()
		if str == '':
			return 0
		str = str.split()[0]
		flag = True
		if str[0] == '+':
			flag = True
			str = str[1:]
		elif str[0] == '-':
			flag = False
			str = str[1:]
		if str == '' or str[0] not in '0123456789':
			return 0
		s = ''
		for ch in str:
			if ch in '0123456789':
				s += ch
			else:
				break
		try:
			result = int(s)
		except:
			return 0
		else:
			if not flag:
				result = -result
		if result > 2147483647:
			result = 2147483647
		elif result < -2147483648:
			result = -2147483648
		return result


class Solution:

	def myAtoi(self, str):
		INT_MAX = 2147483647
		INT_MIN = -2147483648
		str = str.strip()
		if not str:
			return 0
		sign = 1
		if str[0] in ('+', '-'):
			if str[0] == '-':
				sign = -1
			str = str[1:]
		if not str:
			return 0
		if not str[0].isdigit():
			return 0
		for (ind, val) in enumerate(str):
			if not val.isdigit():
				str = str[:ind]
				break
		sum = int(str)
		result = sign * sum
		if result > INT_MAX:
			return INT_MAX
		if result < INT_MIN:
			return INT_MIN
		return result


class Solution:

	def myAtoi(self, s):
		count = 0
		sign = 1
		st = '0'
		s = s.strip()
		for i in range(len(s)):
			if ord(s[i]) >= 48 and ord(s[i]) <= 57:
				st = st + s[i]
			elif s[i] == '+' and count == 0:
				count = 1
			elif s[i] == '+' and count == 1:
				break
			elif s[i] == '-' and count == 0:
				sign = -1
				count = 1
			elif s[i] == '-' and count == 1:
				break
			else:
				break
		n = sign * int(st)
		if n >= 2147483647:
			return 2147483647
		elif n <= -2147483648:
			return -2147483648
		else:
			return n


class Solution:

	def myAtoi(self, str):
		if len(str) == 0:
			return 0
		ls = list(str.strip())
		sign = -1 if ls[0] == '-' else 1
		if ls[0] in ['-', '+']:
			del ls[0]
		(ret, i) = (0, 0)
		while i < len(ls) and ls[i].isdigit():
			ret = ret * 10 + ord(ls[i]) - ord('0')
			i += 1
		return max(-2 ** 31, min(sign * ret, 2 ** 31 - 1))


class Solution:

	def myAtoi(self, str):
		str = str.lstrip()
		if not str:
			return 0
		sign = -1 if str[0] == '-' else 1
		if str[0] in ['+', '-']:
			str = str[1:]
		(i, res) = (0, 0)
		while i < len(str) and str[i].isdigit():
			res = res * 10 + ord(str[i]) - ord('0')
			i += 1
		return max(-2 ** 31, min(2 ** 31 - 1, sign * res))


class Solution:

	def myAtoi(self, str):
		s = str.lstrip()
		if len(s) == 0:
			return 0
		if s[0] not in ['+', '-']:
			sign = 1
			i = 0
			while i < len(s) and s[i].isdigit():
				i += 1
			int_as_str = s[:i]
		else:
			sign = 1 if s[0] == '+' else -1
			i = 1
			while i < len(s) and s[i].isdigit():
				i += 1
			int_as_str = s[1:i]
		if len(int_as_str) == 0:
			return 0
		return max(-2 ** 31, min(sign * int(int_as_str), 2 ** 31 - 1))


class Solution:

	def myAtoi(self, str):
		str = str.strip()
		if len(str) == 0:
			return 0
		if str[0] == '-':
			(ret, i) = (0, 1)
			sign = -1
		elif str[0] == '+':
			(ret, i) = (0, 1)
			sign = 1
		else:
			(ret, i) = (0, 0)
			sign = 1
		while i < len(str) and str[i].isdigit():
			ret = ret * 10 + int(str[i])
			i += 1
		return max(-2 ** 31, min(sign * ret, 2 ** 31 - 1))


class Solution:

	def myAtoi(self, str):
		if not str:
			return 0
		str = str.strip()
		(number, flag) = (0, 1)
		if str[0] == '-':
			str = str[1:]
			flag = -1
		elif str[0] == '+':
			str = str[1:]
		for c in str:
			if c >= '0' and c <= '9':
				number = 10 * number + ord(c) - ord('0')
			else:
				break
		number = flag * number
		number = number if number <= 2147483647 else 2147483647
		number = number if number >= -2147483648 else -2147483648
		return number