003 无重复字符最长子串

public int lengthOfLongestSubstring(String s) {
        Set<Character> occ = new HashSet<Character>();
        int n = s.length();
        int rk = -1, ans = 0;
        for (int i = 0; i < n; i++) {
            if (i != 0) {
                occ.remove(s.charAt(i - 1));
            }
            while (rk + 1 < n && !occ.contains(s.charAt(rk + 1))) {
                occ.add(s.charAt(rk + 1));
                rk++;
            }
            ans = Math.max(rk - i + 1, ans);
        }
        return ans;
    }