Implementing String to Integer Conversion (atoi) – A Step-by-Step Guide leetcode-8

String to Integer (atoi) – A Step-by-Step Guide

Introduction

Converting a string to an integer is a common problem in programming. In this blog, we will walk through a simple approach to implementing the atoi function.

Approach

  • Trim leading whitespace from the string.
  • Check if the first character is a sign (`+` or `-`) and store it.
  • Extract numeric characters and form the number.
  • Convert the numeric string to an integer and apply the sign.
  • Clamp the result within the 32-bit integer range (`[-2147483648, 2147483647]`).

Code Implementation


class Solution:
    def myAtoi(self, s: str) -> int:
        s = s.strip()
        sign = 1
        result = "0"
        for i, c in enumerate(s):
            if i == 0:
                if c == '-':
                    sign = -1
                elif c == '+':
                    sign = 1
                elif c.isdigit():
                    result += c
                else :
                    return 0
            else :
                if not c.isdigit():
                    break
                result += c
        
        if int(result) * sign < -2147483648:
            return -2147483648
        elif int(result) * sign > 2147483647:
            return 2147483647
        else:
            return int(result) * sign

Time and Space Complexity

Time Complexity: O(n) - We traverse the string once.

Space Complexity: O(1) - We use only a few extra variables.

LeetCode Solution

You can check out my LeetCode solution here.

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