MySQL  8.0.18
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depth_first_search.h
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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  vertexes 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 vertexes to which the edges exists.
54  @param [in,out] visited_set A set of vertexes 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 */
58 template <typename TVertex, typename TVisit_start, typename TVisit_end,
59  typename TGet_neighbors, typename TVertex_less = std::less<TVertex>>
60 void 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
task_env * stack
Definition: task.c:881
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 vertexes being an subset of un...
Definition: depth_first_search.h:60