Dictionaries ( dictionary )

Definition

An instance D of the parameterized data type dictionary<K,I> is a collection of items (dic_item). Every item in D contains a key from the linearly ordered data type K, called the key type of D, and an information from the data type I, called the information type of D. The number of items in D is called the size of D. A dictionary of size zero is called the empty dictionary. We use < k, i > to denote an item with key k and information i (i is said to be the information associated with key k). For each k $\in$ K there is at most one i $\in$ I with < k, i > $\in$ D.

#include < LEDA/dictionary.h >

Types

dictionary<K,I>::item	the item type.
dictionary<K,I>::key_type	the key type.
dictionary<K,I>::inf_type	the information type.

Creation

dictionary<K,I>	D	creates an instance D of type dictionary<K,I> based on the linear order defined by the global compare function and initializes it with the empty dictionary.
dictionary<K,I>	D(int (*cmp)(K, K ))	creates an instance D of type dictionary<K,I> based on the linear order defined by the compare function cmp and initializes it with the empty dictionary.

Operations

K	D.key(dic_item it)	returns the key of item it. Precondition it is an item in D.
I	D.inf(dic_item it)	returns the information of item it. Precondition it is an item in D.
I&	D[dic_item it]	returns a reference to the information of item it. Precondition it is an item in D.
dic_item	D.insert(K k, I i)	associates the information i with the key k. If there is an item < k, j > in D then j is replaced by i, else a new item < k, i > is added to D. In both cases the item is returned.
dic_item	D.lookup(K k)	returns the item with key k (nil if no such item exists in D).
I	D.access(K k)	returns the information associated with key k. Precondition there is an item with key k in D.
void	D.del(K k)	deletes the item with key k from D (null operation, if no such item exists).
void	D.del_item(dic_item it)	removes item it from D. Precondition it is an item in D.
void	D.change_inf(dic_item it, I i)
		makes i the information of item it. Precondition it is an item in D.
void	D.clear()	makes D the empty dictionary.
int	D.size()	returns the size of D.
bool	D.empty()	returns true if D is empty, false otherwise.

Iteration STL compatible iterators are provided when compiled with -DLEDA_STL_ITERATORS (see LEDAROOT/demo/stl/dic.c for an example).

Implementation

Dictionaries are implemented by (2, 4)-trees. Operations insert, lookup, del_item, del take time O(log n), key, inf, empty, size, change_inf take time O(1), and clear takes time O(n). Here n is the current size of the dictionary. The space requirement is O(n).

Example

We count the number of occurrences of each string in a sequence of strings.

#include <LEDA/dictionary.h>

main()
{ dictionary<string,int> D;
  string s;
  dic_item it;

  while (cin >> s)
  { it = D.lookup(s);
    if (it==nil) D.insert(s,1);
    else D.change_inf(it,D.inf(it)+1);
  }

  forall_items(it,D) cout << D.key(it) << " : " <<  D.inf(it) << endl;

}