#8字符串转换整数 (atoi)

final class Solution {
    public int myAtoi(String s) {
        if (s == null || s.isEmpty()) return 0;
        int index = 0;
        while (index < s.length() && s.charAt(index) == ' ') index++;

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

        int value = 0;
        while (index < s.length()) {
            char current = s.charAt(index);
            if (current < '0' || current > '9') break;
            int digit = current - '0';
            if (value > (Integer.MAX_VALUE - digit) / 10) {
                return sign > 0 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
            }
            value = value * 10 + digit;
            index++;
        }
        return sign * value;
    }
}