tarjan.cc revision 39910dcd1d68987ccee7c3031dc269233a8490bb 
1//
2// Copyright (C) 2010 The Android Open Source Project
3//
4// Licensed under the Apache License, Version 2.0 (the "License");
5// you may not use this file except in compliance with the License.
6// You may obtain a copy of the License at
7//
8//      http://www.apache.org/licenses/LICENSE-2.0
9//
10// Unless required by applicable law or agreed to in writing, software
11// distributed under the License is distributed on an "AS IS" BASIS,
12// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13// See the License for the specific language governing permissions and
14// limitations under the License.
15//
16#include "update_engine/payload_generator/tarjan.h"
17
18#include <algorithm>
19#include <vector>
20
21#include <base/logging.h>
22
23#include "update_engine/common/utils.h"
24
25using std::min;
26using std::vector;
27
28namespace chromeos_update_engine {
29
30namespace {
31const vector<Vertex>::size_type kInvalidIndex = -1;
32}
33
34void TarjanAlgorithm::Execute(Vertex::Index vertex,
35                              Graph* graph,
36                              vector<Vertex::Index>* out) {
37  stack_.clear();
38  components_.clear();
39  index_ = 0;
40  for (Graph::iterator it = graph->begin(); it != graph->end(); ++it)
41    it->index = it->lowlink = kInvalidIndex;
42  required_vertex_ = vertex;
43
44  Tarjan(vertex, graph);
45  if (!components_.empty())
46    out->swap(components_[0]);
47}
48
49void TarjanAlgorithm::Tarjan(Vertex::Index vertex, Graph* graph) {
50  CHECK_EQ((*graph)[vertex].index, kInvalidIndex);
51  (*graph)[vertex].index = index_;
52  (*graph)[vertex].lowlink = index_;
53  index_++;
54  stack_.push_back(vertex);
55  for (Vertex::EdgeMap::iterator it = (*graph)[vertex].out_edges.begin();
56       it != (*graph)[vertex].out_edges.end(); ++it) {
57    Vertex::Index vertex_next = it->first;
58    if ((*graph)[vertex_next].index == kInvalidIndex) {
59      Tarjan(vertex_next, graph);
60      (*graph)[vertex].lowlink = min((*graph)[vertex].lowlink,
61                                     (*graph)[vertex_next].lowlink);
62    } else if (utils::VectorContainsValue(stack_, vertex_next)) {
63      (*graph)[vertex].lowlink = min((*graph)[vertex].lowlink,
64                                     (*graph)[vertex_next].index);
65    }
66  }
67  if ((*graph)[vertex].lowlink == (*graph)[vertex].index) {
68    vector<Vertex::Index> component;
69    Vertex::Index other_vertex;
70    do {
71      other_vertex = stack_.back();
72      stack_.pop_back();
73      component.push_back(other_vertex);
74    } while (other_vertex != vertex && !stack_.empty());
75
76    if (utils::VectorContainsValue(component, required_vertex_)) {
77      components_.resize(components_.size() + 1);
78      component.swap(components_.back());
79    }
80  }
81}
82
83}  // namespace chromeos_update_engine
84