培训资料 —— 字典树

//an inner class to actually contain values and the next nodes

class TrieNode<T>

{

private Dictionary<char, TrieNode<T>> _next =

new Dictionary<char, TrieNode<T>>();

public ICollection<T> Values { get; private set; }

public TrieNode()

{

this.Values = new List<T>();

_next = new Dictionary<char, TrieNode<T>>();

}

public void AddValue(string key, int depth, T item)

{

if (depth < key.Length)

{

//keep creating/following nodes until

//we reach the end of the key

TrieNode<T> subNode;

if (!_next.TryGetValue(key[depth], out subNode))

{

subNode = new TrieNode<T>();

_next[key[depth]] = subNode;

}

subNode.AddValue(key, depth + 1, item);

}

else

{

Values.Add(item);

}

}

//get the sub-node for the specific character

public TrieNode<T> GetNext(char c)

{

TrieNode<T> node;

if (_next.TryGetValue(c, out node))

return node;

return null;

}

//get all values in this node, and possibly all nodes under this one

public ICollection<T> GetValues(bool recursive)

{

List<T> values = new List<T>();

values.AddRange(this.Values);

if (recursive)

{

foreach (TrieNode<T> node in _next.Values)

{

values.AddRange(node.GetValues(recursive));

}

}

return values;

}

}

大部分功能都在这个字典树节点里面实现了，但是为了方便起见，我们把一些复杂的东西封装了起来。

class Trie<T>

{

TrieNode<T> _root = new TrieNode<T>();

public void AddValue(string key, T item)

{

_root.AddValue(key, 0, item);

}

public ICollection<T> FindValues(string key, bool recursive)

{

TrieNode<T> next = _root;

int index = 0;

//follow the key to the last node

while (index < key.Length &&

next.GetNext(key[index]) != null)

{

next = next.GetNext(key[index++]);

}

//only get values if we found the entire key

if (index == key.Length)

{

return next.GetValues(recursive);

}

else

{

return new T[0];

}

}

}

 

作为一个测试程序，示例代码用一系列单词填充了一个字典树并且用一些方式来查询它。你可以在本章的字典树示例代码工程中来查看这些代码。下面是程序的输出：

Non-recursive lookup:

agonize

Recursive lookup:

agonize

agonized

agonizedlies

agonizedly

agonizer

agonizers

agonizes

Non-existent lookup:

Found 0 values