StringToInteger

Problem

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

Solution

Track the value of the integer as in separate sign and value variables.

Use s.strip() to remove any whitespace.
Check if the string is empty. If so, return 0.
Check the first character of the string. If it is ‘+’ or ‘-’, the number portion of the string starts at 1. Set the sign based on the character or default to a positive sign.
Get all the numeric digits in the string.
From the end, increase value by \(\textrm{digit}_i * 10^i\). If value exceeds the int32 limits of \([-2^{32}, 2^{32} - 1]\), clamp value.

Code

def myAtoi(s: str) -> int:
    """Convert string to integer.
    """
    sign = 1
    value = 0

    s = s.strip()

    if len(s) == 0:
        return 0

    sign_char = s[0]
    num_start = 0
    if sign_char in {'-', '+'}:
        num_start = 1
    if sign_char == '-':
        sign = -1

    num_string = ''
    for char in s[num_start:]:
        if not char.isnumeric():
            break

        num_string += char

    for i, char in enumerate(reversed(num_string)):
        value += int(char) * 10**i
        if sign == 1 and value >= 2**31 - 1:
            return 2**31 - 1
        elif sign == -1 and value >= 2**31:
            return -2**31

    return sign * value

Test

>>> from StringToInteger import myAtoi
>>> myAtoi('42')
42
>>> myAtoi('   -42')
-42
>>> myAtoi('4193 with words')
4193

StringToInteger.myAtoi(s: str) → int: Convert string to integer.