Solution.java

class Solution {
    public int myAtoi(String s) {
        if (s == null || s.length() == 0) return 0;

        s = s.trim();
        if (s.isEmpty()) return 0;

        int index = 0;
        int sign = 1;
        int result = 0;
        int n = s.length();

        if (index < n && (s.charAt(index) == '+' || s.charAt(index) == '-')) {
            sign = (s.charAt(index) == '-') ? -1 : 1;
            index++;
        }

        while (index < n && Character.isDigit(s.charAt(index))) {
            int digit = s.charAt(index) - '0';

            if (result > (Integer.MAX_VALUE - digit) / 10) {
                return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
            }

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

        return result * sign;
    }
}