MegaNasty.java

class Solution {
    public int lengthOfLongestSubstring(String s) {
        
        HashSet<Character> seenSoFar = new HashSet<Character>();
        
        int curLength = 0;
        int longestSoFar = 0;
        int start = 0;
        int end = 0;
        
        for (int i = 0; i < s.length(); i++) {
            
            char curChar = s.charAt(i);
            
            if (seenSoFar.contains(curChar)) {
                longestSoFar = longestSoFar >= curLength ? longestSoFar : curLength;
                if (s.charAt(start) == curChar) {
                    while (start != i && start < i && s.charAt(start) == curChar) {
                        start++;
                        curLength--;
                    }
                    curLength++;
                } else {
                    while (s.charAt(start) != curChar) {
                        seenSoFar.remove(s.charAt(start));
                        start++;
                        curLength--;
                    }
                    start++;
                }
            } else {
                seenSoFar.add(curChar);
                curLength++;
                end++;
            }
            
        }
        
        longestSoFar = longestSoFar >= curLength ? longestSoFar : curLength;
        
        
        return longestSoFar;
    }
}