无重复字符的最长子串

双指针 + 哈希表

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int ans = 0;
        HashSet<Character> hs = new HashSet<>();        
        int l = 0, r = 0;
        while(r < s.length()) {
            if(!hs.contains(s.charAt(r))) {
                hs.add(s.charAt(r));
                ans = Math.max(ans, r - l + 1);
                r ++;
            }
            else {
                while(l < r && hs.contains(s.charAt(r))) {
                    hs.remove(s.charAt(l));
                    l ++;
                }
            }
        }
        return ans;
    }
}