Node Arrays ( node_array )

Definition

An instance A of the parameterized data type node_array<E> is a partial mapping from the node set of a graph G to the set of variables of type E, called the element type of the array. The domain I of A is called the index set of A and A(v) is called the element at position v. A is said to be valid for all nodes in I. The array access operator A[v] checks its precondition (A must be valid for v). The check can be turned off by compiling with the flag -DLEDA_CHECKING_OFF.

#include < LEDA/graph/node_array.h >

Creation

node_array<E>	A	creates an instance A of type node_array<E> with empty index set.
node_array<E>	A(const graph_t& G)	creates an instance A of type node_array<E> and initializes the index set of A to the current node set of graph G.
node_array<E>	A(const graph_t& G, E x)	creates an instance A of type node_array<E>, sets the index set of A to the current node set of graph G and initializes A(v) with x for all nodes v of G.
node_array<E>	A(const graph_t& G, int n, E x)
		creates an instance A of type node_array<E> valid for up to n nodes of graph G and initializes A(v) with x for all nodes v of G. Precondition n > = | V|. A is also valid for the next n - | V| nodes added to G.

Operations

const graph_t&	A.get_graph()	returns a reference to the graph of A.
E&	A[node v]	returns the variable A(v). Precondition A must be valid for v.
void	A.init(const graph_t& G)	sets the index set I of A to the node set of G, i.e., makes A valid for all nodes of G.
void	A.init(const graph_t& G, E x)
		makes A valid for all nodes of G and sets A(v) = x for all nodes v of G.
void	A.init(const graph_t& G, int n, E x)
		makes A valid for at most n nodes of G and sets A(v) = x for all nodes v of G. Precondition n > = | V|. A is also valid for the next n - | V| nodes added to G.
bool	A.use_node_data(const graph_t& G)
		use free data slots in the nodes of G (if available) for storing the entries of A. If no free data slot is available in G, an ordinary node_array<E>is created. The number of additional data slots in the nodes and edges of a graph can be specified in the graph::graph(int n_slots, int e_slots) constructor. The result is true if a free slot is available and false otherwise.
bool	A.use_node_data(const graph_t& G, E x)
		use free data slots in the nodes of G (if available) for storing the entries of A and initializes A(v) = x for all nodes v of G. If no free data slot is available in G, an ordinary node_array<E> is created. The number of additional data slots in the nodes and edges of a graph can be specified in the graph::graph(int n_slots, int e_slots) constructor. The result is true if a free slot is available and false otherwise.

Implementation

Node arrays for a graph G are implemented by C++vectors and an internal numbering of the nodes and edges of G. The access operation takes constant time, init takes time O(n), where n is the number of nodes in G. The space requirement is O(n).

Remark: A node array is only valid for a bounded number of nodes of G. This number is either the number of nodes of G at the moment of creation of the array or it is explicitely set by the user. Dynamic node arrays can be realized by node maps (cf. section Node Maps).