Title Description
Atoi you to implement a function, it can convert a string to an integer.
First, the function will begin with a space character discard useless if necessary, until the find to the first non-space character so far.
When we find the first non-space character is a positive or negative number, the combination of the symbols as much as possible with consecutive numbers up later, as the sign of integer; if the first non-space character is figures, which directly after the continuous numeric characters are combined to form an integer.
In addition to the string after a valid integer part may also exist extra characters, these characters can be ignored, they should not affect a function.
Note: if the character string in the first non-space character is not a valid integer character string is empty or contains only white space character string, then you will not need to be a function of conversion.
In any case, if the function can not effectively convert, 0 is returned.
Description:
We assume that the environment can store 32-bit signed integer size, then the numerical range [-231 231--1]. If the value exceeds this range, return INT_MAX (231 - 1) or INT_MIN (-231).
Example 1:
Input: "42"
Output: 42
Example 2:
Input: "-42"
Output: -42
Explanation: a first non-blank character '-', it is a negative sign.
We will all digital consecutive negative number and later combined as much as possible, and finally get -42.
Example 3:
Input: "4193 with words"
Output: 4193
Explanation: converting the digital OFF '3', because the next character is not numeric.
Example 4:
Input: "words and 987"
Output: 0
Explanation: a first non-blank character 'w', but it is not a positive number or negative number.
Therefore, the conversion can not be performed effectively.
python code
class Solution:
def myAtoi(self, str: str) -> int:
mathList=['-','+','0','1','2','3','4','5','6','7','8','9']
str2 = str.lstrip()
try:
if len(str2)==0 or str2[0] not in mathList:
return 0
else:
for i in range(1, len(str2)):
if str2[i] not in mathList[2:]:
str2 = str2[:i]
break
ans = int(str2)
if ans < 2**31-1 and ans > -2**31:
return ans
else:
return 2**31-1 if ans > 0 else -2**31
except:
return 0
