Exemple #1
0
        // 返回bytes
        public static byte[] Compress(string text)
        {
            BitVirtualSteam bvStream = new BitVirtualSteam();

            char[] chars = text.ToCharArray();
            // 统计频次
            int[] freqs = new int[R];
            for (int i = 0; i < chars.Length; i++)
            {
                freqs[chars[i]]++;
            }
            HuffmanNode root = BuildTrie(freqs);

            // 构造编译表 每个字母 对应一个 code 字符串
            string[] st = new string[R];
            BuildCode(st, root, "");

            List <bool> bits = new List <bool>();

            WriteTrie(bvStream, root);
            bvStream.Write(text.Length);
            // var lenBytes = BitConverter.GetBytes(text.Length);

            // BitArray array = new BitArray(lenBytes);
            // for (int i = 0; i < array.Length; i++)
            // {
            //     bits.Add(array[i]);
            // }

            for (int i = 0; i < text.Length; i++)
            {
                string code = st[text[i]];
                for (int j = 0; j < code.Length; j++)
                {
                    if (code[j] == '1')
                    {
                        bvStream.Write(true);
                    }
                    else
                    {
                        bvStream.Write(false);
                    }
                }
            }

            return(bvStream.GetBytes());
        }
Exemple #2
0
        private static HuffmanNode BuildTrie(int[] freqs)
        {
            // 对字母表进行频次如优先队列
            MinPQ <HuffmanNode> pq = new MinPQ <HuffmanNode>(1000);

            for (char ch = (char)0; ch < R; ch++)
            {
                if (freqs[ch] > 0)
                {
                    pq.Insert(new HuffmanNode(ch, freqs[ch], null, null));
                }
            }

            //合成频率相关最小的树
            while (pq.Count > 1)
            {
                HuffmanNode x      = pq.DelMin();
                HuffmanNode y      = pq.DelMin();
                HuffmanNode parent = new HuffmanNode('\0', x.Freq + y.Freq, x, y);
                pq.Insert(parent);
            }
            return(pq.DelMin());
        }
Exemple #3
0
        public static string Expand(byte[] bytes)
        {
            int             index    = 0;
            BitArray        bits     = new BitArray(bytes);
            BitVirtualSteam bvStream = new BitVirtualSteam(bytes);
            HuffmanNode     root     = ReadTrie(bvStream, ref index);
            BitArray        lenbs    = new BitArray(32);

            for (int i = 0; i < 32; i++)
            {
                lenbs[i] = bits[index++];
            }
            byte[] lenBytes = new byte[4];
            lenbs.CopyTo(lenBytes, 0);
            //int N = BitConverter.ToInt32(lenBytes);
            int N = bvStream.ReadInt();

            char[] chars = new char[N];
            for (int i = 0; i < N; i++)
            {
                HuffmanNode x = root;
                while (!x.isLeaf())
                {
                    //一直往前读取
                    if (bvStream.ReadBoolean())
                    {
                        x = x.Right;
                    }
                    else
                    {
                        x = x.Left;
                    }
                }
                chars[i] = x.Ch;
            }
            return(string.Join("", chars));
        }
Exemple #4
0
 private static string[] BuildCode(HuffmanNode root)
 {
     string[] st = new string[R];
     BuildCode(st, root, "");
     return(st);
 }