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// ==========================================================================
// SeqAn - The Library for Sequence Analysis
// ==========================================================================
// Copyright (c) 2006-2026, Knut Reinert, FU Berlin
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
// * Neither the name of Knut Reinert or the FU Berlin nor the names of
// its contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL KNUT REINERT OR THE FU BERLIN BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
// DAMAGE.
//
// ==========================================================================
// Author: Manuel Holtgrewe <manuel.holtgrewe@fu-berlin.de>
// ==========================================================================
// Implementation of Weakly-Connected-Components algorithm.
// ==========================================================================
#ifndef INCLUDE_SEQAN_GRAPH_ALGORITHMS_WEAKLY_CONNECTED_COMPONENTS_H_
#define INCLUDE_SEQAN_GRAPH_ALGORITHMS_WEAKLY_CONNECTED_COMPONENTS_H_
namespace seqan2 {
// ============================================================================
// Forwards
// ============================================================================
// ============================================================================
// Tags, Classes, Enums
// ============================================================================
// ============================================================================
// Metafunctions
// ============================================================================
// ============================================================================
// Functions
// ============================================================================
// ----------------------------------------------------------------------------
// Function weaklyConnectedComponents()
// ----------------------------------------------------------------------------
/*!
* @fn weaklyConnectedComponents
* @headerfile <seqan/graph_algorithms.h>
* @brief Compute weakly connected components of a directed graph.
*
* @signature TSize weaklyConnectedComponents(components, g);
*
* @param[out] components
* A property map. Each vertex is mapped to a component id. If two vertices share the same id they
* are in the same component.
* @param[in] g A @link DirectedGraph @endlink to use for the input.
*
* @return TSize The number of weakly connected components (Metafunction: @link Graph#Size @endlink of the type
* of <tt>g</tt>).
*
* The running time is <tt>O(n a(n, n))</tt> where <tt>a</tt> is the inverse Ackermann function and thus almost linear.
* The union find data structure is used since the graph implementations do not allow the efficient iteration of
* in-edges.
*/
template <typename TSpec, typename TComponents>
typename Size<Graph<TSpec> >::Type
weaklyConnectedComponents(TComponents & components,
Graph<TSpec> const & g)
{
typedef Graph<TSpec> TGraph;
typedef typename Size<TGraph>::Type TSize;
typedef typename Iterator<TGraph, EdgeIterator>::Type TEdgeIterator;
typedef typename Iterator<TGraph, VertexIterator>::Type TVertexIterator;
typedef typename VertexDescriptor<TGraph>::Type TVertexDescriptor;
// Initialization.
UnionFind<TVertexDescriptor> unionFind;
resizeVertexMap(unionFind, g);
// Iterate over all edges, joining weakly connected components.
for (TEdgeIterator itE(g); !atEnd(itE); goNext(itE))
joinSets(unionFind, findSet(unionFind, sourceVertex(itE)), findSet(unionFind, targetVertex(itE)));
// Count number of sets.
TSize setCount = 0;
for (TVertexIterator itV(g); !atEnd(itV); goNext(itV))
setCount += (findSet(unionFind, *itV) == *itV);
// Build a map from graph vertex descriptor to component id.
TSize nextId = 0;
clear(components);
resizeVertexMap(components, g, setCount); // setCount is sentinel value
for (TVertexIterator itV(g); !atEnd(itV); goNext(itV)) {
if (getProperty(components, findSet(unionFind, *itV)) == setCount)
assignProperty(components, findSet(unionFind, *itV), nextId++);
assignProperty(components, *itV, getProperty(components, findSet(unionFind, *itV)));
}
return setCount;
}
} // namespace seqan2
#endif // #ifndef INCLUDE_SEQAN_GRAPH_ALGORITHMS_WEAKLY_CONNECTED_COMPONENTS_H_
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