76. Minimum Window Substring

   public string MinWindow(string s, string t) {
        if(t==null || t == "" || s == "") return t;
        if(t.Length > s.Length) return "";
        int max =s.Length+1;
        var res ="";
        var hashtable = new Dictionary<char,int>();
        int min =s.Length;
        for(int i =0;i< t.Length;i++)
        {
            if(hashtable.ContainsKey(t[i])) hashtable[t[i]]++;
            else hashtable.Add(t[i],1);
        }
        
        for(int i = 0;i<=s.Length - t.Length;i++)
        {
            var exist = new Dictionary<char,int>();
            int count =0;
            for(int j = i;j<s.Length;j++)
            {
                if(max < j-i+1) break;
                if(hashtable.ContainsKey(s[j]))
                {
                    if(exist.ContainsKey(s[j]))
                    {
                        if(exist[s[j]] < hashtable[s[j]])
                        {
                            count++;
                            exist[s[j]]++;
                            if(count >= t.Length)
                            {
                                if(max > j-i+1) {res =s.Substring(i,j-i+1);max = j-i+1;}
                                break;
                            }
                        }
                    }
                    else
                    {
                        count++;
                        exist.Add(s[j],1);
                        if(count >= t.Length) 
                        {
                            if(max > j-i+1) {res =s.Substring(i,j-i+1);max = j-i+1;}
                                break;
                        }
                    }
                }
            }
        }
        return res;
    }

public string MinWindow(string s, string t) {
        if(t==null || t == "" ||s==mull|| s == "") return t;
        if(t.Length > s.Length) return "";
        int max =s.Length+1;
        var res ="";
        var hashtable = new Dictionary<char,int>();
        for(int i =0;i< t.Length;i++)
        {
            if(hashtable.ContainsKey(t[i])) hashtable[t[i]]++;
            else hashtable.Add(t[i],1);
        }
        
        int left =0;
        int right =-1;
        int count = 0;
        while(right<s.Length)
        {
            if(count == t.Length)
            {
                if(max > right - left + 1)
                {
                    max= right - left + 1;
                    res = s.Substring(left,right - left + 1);
                }
                if(hashtable.ContainsKey(s[left]))
                {
                    if(hashtable[s[left]] ==0)  count--;
                    hashtable[s[left]]++;
                   
                }
               
                left++;
            }
            else if(right<s.Length-1)
            {
                right++;
                if(hashtable.ContainsKey(s[right]) )
                {
                    if(hashtable[s[right]]>0) count++;
                    hashtable[s[right]]--;
                }
            }
            else right++;
            
        }
        return res;

    }