LeetCode 2 Find longest subsequence in string non repeating

longestSubsequenceNonRepeating.java

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int l = 0;
        int result = 0;
        Set<Character> set = new HashSet<>();
        // We start with right pointer from 0, both left and right are at 0!.
        for (int r = 0; r < s.length(); r++) { 
            // As long as we have duplicates move left first. Trick! at first 0,0 no duplicates!
            while (set.contains(s.charAt(r))) { 
                set.remove(s.charAt(l)); // Note we remove what left points to! until we remove all duplicates with left.
                l++;
            }
            // Now add current different r into the set.
            set.add(s.charAt(r));
            // Trick! Note that when r = l = 0 then s is also empty and we would put in result 0 - 0 + 1 !
            result = Math.max(result, r - l + 1);
        }
        return result;
    }
}