Problem Statement

Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer.

The algorithm for myAtoi(string s) is as follows:

1. Whitespace: Ignore any leading whitespace (" ").
2. Signedness: Determine the sign by checking if the next character is '-' or '+', assuming positivity if neither present.
3. Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read, then the result is 0.
4. Rounding: If the integer is out of the 32-bit signed integer range [-2^31, 2^31 - 1], then round the integer to remain in the range. Specifically, integers less than -2^31 should be rounded to -2^31, and integers greater than 2^31 - 1 should be rounded to 2^31 - 1.
   Return the integer as the final result.

Examples

Example 1:

Different Approaches

1️⃣ Iteration

Code:

#include <climits>
#include <string>
using namespace std;

class Solution {
public:
    int myAtoi(string s) {

        // Initialize variables
        int index = 0; // Pointer to traverse the string
        int length = s.length(); // Length of the input string
        int result = 0; // Holds the final integer value
        bool isNegative = false; // Flag to determine if the number is negative

        // Step 1: Skip leading whitespaces
        while (index < length && s[index] == ' ') {
            index++;
        }

        // Step 2: Check for a sign
        if (index < length && (s[index] == '-' || s[index] == '+')) {
            isNegative = (s[index] == '-');
            index++;
        }

        // Step 3: Convert digits to integer
        while (index < length && s[index] >= '0' && s[index] <= '9') {
            int digit = s[index] - '0';

            // Step 4: Handle overflow
            if (result > (INT_MAX - digit) / 10) {
                return isNegative ? INT_MIN : INT_MAX;
            }

            result = result * 10 + digit;
            index++;
        }

        // Step 5: Apply the sign
        return isNegative ? -result : result;
    }
};