3. Longest Substring Without Repeating Characters

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        if(s == null)
            return 0;
        
        int maxLen = 0;
        
        Map<Character, Integer> ind = new HashMap<Character, Integer>();
        
        for(int i = 0; i< s.length(); ++i)
        {
            Character c = s.charAt(i);
            Integer location = ind.get(c);
            if(location == null)
            {
                ind.put(c, i);
            }
            else
            {
                Integer curLen = ind.size();
                if(curLen > maxLen)
                {
                    maxLen = curLen;
                }
                Map<Character, Integer> ind2 = new HashMap<Character, Integer>();
                for(int j = location+1;j<=i;++j)
                {
                    ind2.put(s.charAt(j), j);
                }
                ind = ind2;
                
            }
        }
        Integer curLen = ind.size();
        if(curLen > maxLen)
        {
            maxLen = curLen;
        }
        return maxLen;
    }
}

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        if(s == null)
            return 0;
        
        int maxLen = 0;
        int start = 0; //improvement: instead of constructing a new map. Modify the original map by removing bad part.
        Map<Character, Integer> ind = new HashMap<Character, Integer>();
        
        for(int i = 0; i< s.length(); ++i)
        {
            Character c = s.charAt(i);
            Integer location = ind.get(c);
            if(location == null)
            {
                ind.put(c, i);
            }
            else
            {
                Integer newStart = location+1;
                Integer curLen = ind.size();
                if(curLen > maxLen)
                {
                    maxLen = curLen;
                }
                for(int j = start;j<newStart;++j)
                {
                    ind.remove(s.charAt(j));  //Improvement: remove bad part.
                }
                ind.put(c, i);
                start = newStart;
            }
        }
        Integer curLen = ind.size();
        if(curLen > maxLen)
        {
            maxLen = curLen;
        }
        return maxLen;
    }
}

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        if(s == null)
            return 0;
        
        if (s.length()==0) return 0;
        HashMap<Character, Integer> map = new HashMap<Character, Integer>();
        int max=0;
        for (int i=0, j=0; i<s.length(); ++i){
            Character c = s.charAt(i);
            Integer location = map.get(c);
            if (location != null){
                j = Math.max(j, location + 1); //j points to START.
            }
            map.put(c,i);
            max = Math.max(max,i-j+1);
        }
        return max;
    }
}