Minimum Window Substring

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Java code:
  public static String minWindow (String S, String T)
    {
     if ( S.length() < T.length() || T.isEmpty())
         return "";
   
     int min = 0;
     int start = 0;
     int end = 0;
   
     HashMap<String, Queue<Integer>> window = new  HashMap<String, Queue<Integer>>();
     ArrayList<Integer> index = new ArrayList<Integer> ();
   
     ArrayList<String> tmpT = new ArrayList<String> ();
   
     for (int j = 0; j < T.length(); j++)
     {
        tmpT.add(T.substring(j, j+1));
     }
   
     for (int i = 0; i < S.length(); i++)
     {
       if (T.contains( S.substring(i, i+1)))
       {
           if (tmpT.contains(S.substring(i, i+1)))
           {
               Queue<Integer> tmp = window.get(S.substring(i, i+1));
             
               if (tmp == null)
               {
                tmp = new LinkedList<Integer> ();
               }
             
               tmp.add(i);
               window.put(S.substring(i, i+1), tmp );
               tmpT.remove(S.substring(i,i+1));
             
               index.add(i);
             
               if (tmpT.isEmpty())
               {
                min = index.get( index.size() - 1)- index.get(0);
                start = index.get(0);
                end = index.get( index.size() - 1 );
               }
           }
           else
           {
               Queue<Integer> tmp = window.get(S.substring(i, i+1));
               tmp.add(i);
               index.remove( index.indexOf(tmp.poll()));
               index.add(i);
               window.put(S.substring(i, i+1), tmp);
           }
         
           /**
            * update the min widow.
            */
         
           if (tmpT.isEmpty())
           {
            if ( min > index.get( index.size() - 1)- index.get(0) )
               {
                start = index.get(0);
                end = index.get(index.size() - 1);
                min = index.get( index.size() - 1)- index.get(0);
               }
           }
       }
     
     }
  
     if( !tmpT.isEmpty() )
         return "";
   
    else return S.substring(start, end+1);
   
    }