3. Longest Substring Without Repeating Characters

class Solution {
    public int lengthOfLongestSubstring(String s) {
        Set<Character> ch = new HashSet<Character>();
        
        int result = 0;
        int st = 0, en = 0;
        
        
        while (st < s.length() && en < s.length()) {
            if (!ch.contains(s.charAt(en))) {
                ch.add(s.charAt(en));
                en++;
                result = Math.max(result, en - st);
            } else {
                ch.remove(s.charAt(st));
                st++;
            }
        }
        
        return result;
       
    }
}

Runtime: 6 ms, faster than 68.32% of Java online submissions for Longest Substring Without Repeating Characters.
Memory Usage: 39.2 MB, less than 56.34% of Java online submissions for Longest Substring Without Repeating Characters.

하나하나씩 영역확장해나가는~ 그런느낌