http://leetcode.com/onlinejudge#question_3 http://leetcode.com/2011/05/longest-substring-without-repeating-characters.html

LongestSubstringO(n)

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