# 8. String to Integer (atoi)

https://leetcode.com/problems/string-to-integer-atoi/

###### Medium

##### Description
> Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer (similar to C/C++'s atoi function).
>
> The algorithm for myAtoi(string s) is as follows:
>
> Read in and ignore any leading whitespace.
> Check if the next character (if not already at the end of the string) is '-' or '+'. Read this character in if it is either. This determines if the final result is negative or positive respectively. Assume the result is positive if neither is present.
> Read in next the characters until the next non-digit charcter or the end of the input is reached. The rest of the string is ignored.
> Convert these digits into an integer (i.e. "123" -> 123, "0032" -> 32). If no digits were read, then the integer is 0. Change the sign as necessary (from step 2).
> If the integer is out of the 32-bit signed integer range [-231, 231 - 1], then clamp the integer so that it remains in the range. Specifically, integers less than -231 should be clamped to -231, and integers greater than 231 - 1 should be clamped to 231 - 1.
> Return the integer as the final result.
> Note:
>
> Only the space character ' ' is considered a whitespace character.
> Do not ignore any characters other than the leading whitespace or the rest of the string after the digits.
##### Example
> Input: str = "42"
> Output: 42
> Explanation: The underlined characters are what is read in, the caret is the current reader position.
> Step 1: "42" (no characters read because there is no leading whitespace)
> ^
> Step 2: "42" (no characters read because there is neither a '-' nor '+')
> ^
> Step 3: "42" ("42" is read in)
> ^
> The parsed integer is 42.
> Since 42 is in the range [-231, 231 - 1], the final result is 42.

##### Solution

class Solution:
    def myAtoi(self, s: str) -> int:
        
        result = 0
        sign = 1
        start = False

        for c in s:

            if c.isdigit():
                if not start:
                    start = True
                result = result*10 + int(c)
            else:
                if c == ' ' and not start:
                    continue
                if c == '+' and not start:
                    start = True
                    sign = 1
                    continue
                if c == '-' and not start:
                    start = True
                    sign = -1
                    continue
                break

        limit = result*sign

        if limit > 2**31 -1:
            limit = 2**31 -1
        if limit < -2**31:
            limit = -2**31

        return limit