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/*============================================================================
CMake - Cross Platform Makefile Generator
Copyright 2000-2009 Kitware, Inc., Insight Software Consortium
Distributed under the OSI-approved BSD License (the "License");
see accompanying file Copyright.txt for details.
This software is distributed WITHOUT ANY WARRANTY; without even the
implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
See the License for more information.
============================================================================*/
#include "cmComputeComponentGraph.h"
#include <algorithm>
#include <assert.h>
//----------------------------------------------------------------------------
cmComputeComponentGraph::cmComputeComponentGraph(Graph const& input):
InputGraph(input)
{
// Identify components.
this->Tarjan();
// Compute the component graph.
this->ComponentGraph.resize(0);
this->ComponentGraph.resize(this->Components.size());
this->TransferEdges();
}
//----------------------------------------------------------------------------
cmComputeComponentGraph::~cmComputeComponentGraph()
{
}
//----------------------------------------------------------------------------
void cmComputeComponentGraph::Tarjan()
{
int n = static_cast<int>(this->InputGraph.size());
TarjanEntry entry = {0,0};
this->TarjanEntries.resize(0);
this->TarjanEntries.resize(n, entry);
this->TarjanComponents.resize(0);
this->TarjanComponents.resize(n, -1);
this->TarjanWalkId = 0;
this->TarjanVisited.resize(0);
this->TarjanVisited.resize(n, 0);
for(int i = 0; i < n; ++i)
{
// Start a new DFS from this node if it has never been visited.
if(!this->TarjanVisited[i])
{
assert(this->TarjanStack.empty());
++this->TarjanWalkId;
this->TarjanIndex = 0;
this->TarjanVisit(i);
}
}
}
//----------------------------------------------------------------------------
void cmComputeComponentGraph::TarjanVisit(int i)
{
// We are now visiting this node.
this->TarjanVisited[i] = this->TarjanWalkId;
// Initialize the entry.
this->TarjanEntries[i].Root = i;
this->TarjanComponents[i] = -1;
this->TarjanEntries[i].VisitIndex = ++this->TarjanIndex;
this->TarjanStack.push(i);
// Follow outgoing edges.
NodeList const& nl = this->InputGraph[i];
for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
{
int j = *ni;
// Ignore edges to nodes that have been reached by a previous DFS
// walk. Since we did not reach the current node from that walk
// it must not belong to the same component and it has already
// been assigned to a component.
if(this->TarjanVisited[j] > 0 &&
this->TarjanVisited[j] < this->TarjanWalkId)
{
continue;
}
// Visit the destination if it has not yet been visited.
if(!this->TarjanVisited[j])
{
this->TarjanVisit(j);
}
// If the destination has not yet been assigned to a component,
// check if it has a better root for the current object.
if(this->TarjanComponents[j] < 0)
{
if(this->TarjanEntries[this->TarjanEntries[j].Root].VisitIndex <
this->TarjanEntries[this->TarjanEntries[i].Root].VisitIndex)
{
this->TarjanEntries[i].Root = this->TarjanEntries[j].Root;
}
}
}
// Check if we have found a component.
if(this->TarjanEntries[i].Root == i)
{
// Yes. Create it.
int c = static_cast<int>(this->Components.size());
this->Components.push_back(NodeList());
NodeList& component = this->Components[c];
// Populate the component list.
int j;
do
{
// Get the next member of the component.
j = this->TarjanStack.top();
this->TarjanStack.pop();
// Assign the member to the component.
this->TarjanComponents[j] = c;
this->TarjanEntries[j].Root = i;
// Store the node in its component.
component.push_back(j);
} while(j != i);
// Sort the component members for clarity.
std::sort(component.begin(), component.end());
}
}
//----------------------------------------------------------------------------
void cmComputeComponentGraph::TransferEdges()
{
// Map inter-component edges in the original graph to edges in the
// component graph.
int n = static_cast<int>(this->InputGraph.size());
for(int i=0; i < n; ++i)
{
int i_component = this->TarjanComponents[i];
NodeList const& nl = this->InputGraph[i];
for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
{
int j = *ni;
int j_component = this->TarjanComponents[j];
if(i_component != j_component)
{
this->ComponentGraph[i_component].push_back(j_component);
}
}
}
}
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