8. String to Integer (atoi)

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

Example

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Input: s = “1337c0d3”
Output: 1337
Explanation:
Step 1: “1337c0d3” (no characters read because there is no leading whitespace)
Step 2: “1337c0d3” (no characters read because there is neither a ‘-‘ nor ‘+’)
Step 3: “1337c0d3” (“1337” is read in; reading stops because the next character is a non-digit)

💻 Code

Approach :
- Ignore every comming string elements.
- Make sure set the Max & Min range.
- check sign first, and integers.

• TC : O(n)
• SC: O(1)

class Solution:
    def myAtoi(self, s: str) -> int:
        max_int = 2**31 - 1
        min_int = -2**31

        i = 0   # current index
        n = len(s)

        # Step 1: Whitespace exists, then move current index
        while i < n and s[i] == ' ':
            i += 1
        
        # Step 2: recognizing positive (1) or negative (-1)
        # Check the very first sign only!
        sign = 1
        if i < n and (s[i] == '+' or s[i] == '-'):
            if s[i] == '-':
                sign = -1
            i += 1

        # Step 3: now we check integers only
        result = 0
        while i < n and s[i].isdigit():
            result = result * 10 + int(s[i])    # convert str -> int
            i += 1

        result *= sign

        # checking the range validation
        if result < min_int:
            return min_int
        if result > max_int:
            return max_int

        return result