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string-to-integer-atoi.py
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string-to-integer-atoi.py
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# Time: O(n)
# Space: O(1)
#
# 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.
#
# 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
"""
INT_MAX = 2147483647
INT_MIN = -2147483648
result = 0
if not str:
return result
i = 0
while i < len(str) and str[i].isspace():
i += 1
if len(str) == i:
return result
sign = 1
if str[i] == "+":
i += 1
elif str[i] == "-":
sign = -1
i += 1
while i < len(str) and '0' <= str[i] <= '9':
if result > (INT_MAX - int(str[i])) / 10:
return INT_MAX if sign > 0 else INT_MIN
result = result * 10 + int(str[i])
i += 1
return sign * result