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Depth First Search (flexible) ( GIT_DFS )

Definition

An instance algorithm of class GIT_DFS< OutAdjIt, Stacktype, Mark > is an implementation of an algorithm that traverses a graph in a depth first order. The stack used for the search must be provided by the caller and contains the source(s) of the search.

A next step may return a state which describes the last action. There are the following three possibilities:

  1. dfs_shrink: an adjacency iterator was popped from the stack, i.e. the treewalk returns in root-direction
  2. dfs_leaf: same as dfs_shrink, but a leaf occured
  3. dfs_grow_depth: a new adjacency iterator was appended to the stack because it was detected as not seen before, i.e. the treewalk goes in depth-direction
  4. dfs_grow_breadth: the former current adjacency iterator was replaced by the successor iterator, i.e. the treewalk goes in breadth-direction

Iterator version: There is an iterator version of this algorithm: DFS_It. Usage is similar to that of node iterators without the ability to go backward in the sequence.

#include < LEDA/graph/graph_iterator.h >

Creation

GIT_DFS< OutAdjIt, Stacktype, Mark > algorithm(const Stacktype& st, Mark& ma)
    creates an instance algorithm of this class bound to the stack st and data accessor ma.

Preconditions:

GIT_DFS< OutAdjIt, Stacktype, Mark > algorithm(const Stacktype& st, Mark& ma, const OutAdjIt& ai)
    creates an instance algorithm of this class bound to the stack st, data accessor ma and the adjacency iterator ai representing the source node of the depth first traversal.

Operations

void algorithm.next_unseen() Performs one iteration of the core loop of the algorithm for one unseen node of the graph.

dfs_return algorithm.next() Performs one iteration of the core loop of the algorithm.

OutAdjIt algorithm.current() returns the ``current'' iterator.

void algorithm.finish_algo() executes the algorithm until finished() is true, i.e. exactly if the stack is empty.

bool algorithm.finished() returns true if the internal stack is empty.

void algorithm.init(OutAdjIt s)
    initializes the internal stack with s.

Stacktype& algorithm.get_stack() gives direct access to internal stack.

Implementation

Each operation requires constant time. Therefore, a normal depth-first search needs $ \cal {O}$(m + n) time.


next up previous contents index
Next: Topological Sort (flexible) ( Up: Graphs and Iterators Previous: Breadth First Search (flexible)   Contents   Index
root 2008-01-09