003. Longest Substring Without Repeating Characters

/****
Given a string, find the length of the longest substring without repeating characters.
E.g.:
Given "abcabcbb", the answer is "abc", which the length is 3.
Given "bbbbb", the answer is "b", with the length of 1.
Given "pwwkew", the answer is "wke", with the length of 3. 
Note that the answer must be a substring, "pwke" is a subsequence and not a substring.
****/

//Java solution:

public class Solution {
    public int lengthOfLongestSubstring(String s) {
     if(s.length() == 0 || s == null) {return 0;}
     
     int result = 0;
     int[] map = new int[256]; // map from character's ASCII to its last occured index 
     int j = 0;
     
     for(int i = 0; i < s.length(); i++){
         for(; j < s.length() && map[s.charAt(j)] == 0; j++){
             map[s.charAt(j)] = 1;
             result = Math.max(result, (j-i+1));
         }
         map[s.charAt(i)] = 0;
     }
     
     return result;
    }
}