// 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());
}
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());
}
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));
}
private static string[] BuildCode(HuffmanNode root)
{
string[] st = new string[R];
BuildCode(st, root, "");
return(st);
}
