@Override
    public int compare(HuffmanNode o1, HuffmanNode o2) {
        if(o1.freq < o2.freq){
            return -1;
        }else{
            return 1;
        }
    }
http://www.geeksforgeeks.org/greedy-algorithms-set-3-huffman-coding/
http://www.geeksforgeeks.org/greedy-algorithms-set-3-huffman-coding-set-2/
src/com/interview/tree/HuffmanEncoding.java