blob: 6591fb1d32b52ed3fe448a9885b22967f1eeccf1 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
|
/* Distributed under the OSI-approved BSD 3-Clause License. See accompanying
file Copyright.txt or https://cmake.org/licensing for details. */
#include "cmComputeComponentGraph.h"
#include <algorithm>
#include <cassert>
cmComputeComponentGraph::cmComputeComponentGraph(Graph const& input)
: InputGraph(input)
{
}
cmComputeComponentGraph::~cmComputeComponentGraph() = default;
void cmComputeComponentGraph::Compute()
{
// Identify components.
this->Tarjan();
// Compute the component graph.
this->ComponentGraph.resize(0);
this->ComponentGraph.resize(this->Components.size());
this->TransferEdges();
}
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.
EdgeList const& nl = this->InputGraph[i];
for (cmGraphEdge const& ni : nl) {
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.emplace_back();
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];
EdgeList const& nl = this->InputGraph[i];
for (cmGraphEdge const& ni : nl) {
int j = ni;
int j_component = this->TarjanComponents[j];
if (i_component != j_component) {
// We do not attempt to combine duplicate edges, but instead
// store the inter-component edges with suitable multiplicity.
this->ComponentGraph[i_component].emplace_back(
j_component, ni.IsStrong(), ni.IsCross(), ni.GetBacktrace());
}
}
}
}
|
