http://leetcode.com/onlinejudge#question_3

LongestSubstringBruteForce

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        // Start typing your Java solution below
        // DO NOT write main() function
        String longest = "";
        for(int i = 0; i < s.length(); i++) {
            HashSet<Character> set = new HashSet<Character>();
            set.add(s.charAt(i));
            int j;
            for(j = i + 1; j < s.length(); j++) {
                char current = s.charAt(j);
                if(set.contains(current)) {
                    break;
                } else {
                    set.add(current);
                }
            }
            if(j - i > longest.length()) {
                longest = s.substring(i, j);
            }
        }
        return longest.length();
    }
}