3. 无重复字符的最长子串

public int lengthOfLongestSubstring(String s) {
        if (s == null || s.length() == 0) {
            return 0;
        }
        int max = 0;
        int length = 0;
        HashMap<Character, Integer> h = new HashMap();
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (h.containsKey(c)) {
                i = h.get(c);
                h.clear();
                length = 0;
                continue;
            } else {
                length++;
            }
            h.put(c, i);
            max = Math.max(max, length);
        }
        return max;
    }