MySQL 8.0.32
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depth_first_search.h
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1/*
2 Copyright (c) 2016, 2022, Oracle and/or its affiliates.
3
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16 but WITHOUT ANY WARRANTY; without even the implied warranty of
17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 GNU General Public License, version 2.0, for more details.
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22 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
23*/
24
25#ifndef DEPTH_FIRST_SEARCH_INCLUDED
26#define DEPTH_FIRST_SEARCH_INCLUDED
27
28#include <functional>
29#include <set>
30#include <stack>
31#include <tuple>
32
33/**
34 @file include/depth_first_search.h
35*/
36
37/**
38 Performs a Depth First Search algorithm on a graph defined by a set of
39 vertices being an subset of universum of values of TVertex type and, and set
40 of directed edges generated on demand by get_neighbors() method supplied.
41 Search starts with a selected vertex, for each vertex that is encountered a
42 visitor_start() method supplied is called and when the DFS finishes traversal
43 from that vertex, a visitor_end() method is called. The set of visited nodes
44 is maintained, so the input graph don't have to be a Directed Acyclic Graph.
45
46 @param start_vertex A vertex to start a search from.
47 @param visitor_start A method or lambda that will be called when a specified
48 vertex starts to be processed, the vertex is supplied as the only argument.
49 @param visitor_end A method or lambda that will be called when a specified
50 vertex ends to be processed, i.e. all its neighbors were already processed,
51 the vertex is supplied as the only argument.
52 @param get_neighbors A method or lambda that takes a vertex as an argument and
53 returns a enumerable list of all vertices to which the edges exists.
54 @param [in,out] visited_set A set of vertices that were visited. This can be
55 used to run multiple DFS runs and assure any vertex will not be visited more
56 than once.
57*/
58template <typename TVertex, typename TVisit_start, typename TVisit_end,
59 typename TGet_neighbors, typename TVertex_less = std::less<TVertex>>
60void depth_first_search(TVertex start_vertex, TVisit_start visitor_start,
61 TVisit_end visitor_end, TGet_neighbors get_neighbors,
62 std::set<TVertex> &visited_set = std::set<TVertex>{}) {
63 /* A constant for a index denoting if the search from specified vertex has
64 just been started of just ends. */
65 constexpr int START_VISITING = 0;
66 /* A constant for a index denoting the vertex. */
67 constexpr int CURRENT_VERTEX = 1;
68
69 /* An actual stack for search. */
70 std::stack<std::tuple<bool, TVertex>> stack;
71 /* Check if this vertex was not already visited - this may happen if
72 the visited_set was returned by another DFS run. */
73 if (!visited_set.insert(start_vertex).second) {
74 return;
75 }
76 stack.emplace(true, start_vertex);
77
78 while (!stack.empty()) {
79 std::tuple<bool, TVertex> &elem = stack.top();
80 if (std::get<START_VISITING>(elem)) {
81 visitor_start(std::get<CURRENT_VERTEX>(elem));
82
83 std::get<START_VISITING>(elem) = false;
84 for (TVertex neighbor : get_neighbors(std::get<CURRENT_VERTEX>(elem))) {
85 /* Check if this vertex was not visited yet in this or previous runs. */
86 if (visited_set.insert(neighbor).second) {
87 stack.emplace(true, neighbor);
88 }
89 }
90 } else {
91 visitor_end(std::get<CURRENT_VERTEX>(elem));
92 stack.pop();
93 }
94 }
95}
96
97#endif
void depth_first_search(TVertex start_vertex, TVisit_start visitor_start, TVisit_end visitor_end, TGet_neighbors get_neighbors, std::set< TVertex > &visited_set=std::set< TVertex >{})
Performs a Depth First Search algorithm on a graph defined by a set of vertices being an subset of un...
Definition: depth_first_search.h:60
task_env * stack
Definition: task.cc:875