MyAtoi.java

package com.thealgorithms.strings;

/**
 * A utility class that provides a method to convert a string to a 32-bit signed integer (similar to C/C++'s atoi function).
 */
public final class MyAtoi {
    private MyAtoi() {
    }

    /**
     * Converts the given string to a 32-bit signed integer.
     * The conversion discards any leading whitespace characters until the first non-whitespace character is found.
     * Then, it takes an optional initial plus or minus sign followed by as many numerical digits as possible and interprets them as a numerical value.
     * The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.
     *
     * If the number is out of the range of a 32-bit signed integer:
     * - Returns {@code Integer.MAX_VALUE} if the value exceeds {@code Integer.MAX_VALUE}.
     * - Returns {@code Integer.MIN_VALUE} if the value is less than {@code Integer.MIN_VALUE}.
     *
     * If no valid conversion could be performed, a zero is returned.
     *
     * @param s the string to convert
     * @return the converted integer, or 0 if the string cannot be converted to a valid integer
     */
    public static int myAtoi(String s) {
        if (s == null || s.isEmpty()) {
            return 0;
        }

        s = s.trim();
        int length = s.length();
        if (length == 0) {
            return 0;
        }

        int index = 0;
        boolean negative = false;

        // Check for the sign
        if (s.charAt(index) == '-' || s.charAt(index) == '+') {
            negative = s.charAt(index) == '-';
            index++;
        }

        int number = 0;
        while (index < length) {
            char ch = s.charAt(index);
            if (!Character.isDigit(ch)) {
                break;
            }

            int digit = ch - '0';

            // Check for overflow
            if (number > (Integer.MAX_VALUE - digit) / 10) {
                return negative ? Integer.MIN_VALUE : Integer.MAX_VALUE;
            }

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

        return negative ? -number : number;
    }
}