longest-substring-without-duplicate-characters

public class LengthOfLongestSubstring {
    public static int lengthOfLongestSubstring(String s) {
        if (s == null) {
            return 0;
        }
        Map<Character, Integer> map = new HashMap<>();
        int maxLength = 0;
        int start = 0;
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            Integer duplicateIndex = map.put(c, i);
            if (duplicateIndex != null) {
                if (duplicateIndex >= start) {
                    maxLength = Math.max(maxLength, i - start);
                    start = duplicateIndex + 1;
                }
            }
        }
        return Math.max(maxLength, s.length() - start);
    }

    public static void main(String[] args) {
        int maxLength = lengthOfLongestSubstring("abcabcbb"); // 3
        System.out.println(maxLength);

        maxLength = lengthOfLongestSubstring("bbbbb"); // 1
        System.out.println(maxLength);

        maxLength = lengthOfLongestSubstring("b"); // 1
        System.out.println(maxLength);

        maxLength = lengthOfLongestSubstring(""); // 0
        System.out.println(maxLength);

        maxLength = lengthOfLongestSubstring(null); // 0
        System.out.println(maxLength);
    }
}