src/main/java/com/fishercoder/solutions/_8.java

package com.fishercoder.solutions;

public class _8 {

    public static class Solution1 {
        /**
         * four corner cases:
         * 1. discards all leading zeroes
         * 2. sign of the number
         * 3. overflow
         * 4. invalid input
         */
        public int myAtoi(String s) {
            int pointer = 0;
            int result = 0;
            while (pointer < s.length() && Character.isWhitespace(s.charAt(pointer))) {
                pointer++;
            }
            if (pointer == s.length()) {
                return 0;
            }
            boolean negativeFlag = (s.charAt(pointer) == '-');
            if (s.charAt(pointer) == '+' || s.charAt(pointer) == '-') {
                pointer++;
            }
            for (; pointer < s.length(); pointer++) {
                if (s.charAt(pointer) > '9' || s.charAt(pointer) < '0') {
                    break;
                } else {
                    int digit = s.charAt(pointer) - '0';
                    if (!negativeFlag && result > (Integer.MAX_VALUE - digit) / 10) {
                        return Integer.MAX_VALUE;
                    } else if (negativeFlag && result < (Integer.MIN_VALUE + digit) / 10) {
                        return Integer.MIN_VALUE;
                    }
                    result = result * 10 + (negativeFlag ? -digit : digit);
                }
            }
            return result;
        }
    }

}