Fix vector insertion complexity from O(N) to O(1)

boostorg · Jan 15, 2025 · 836919b · 836919b
1 parent 8e60387
commit 836919b
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Showing 3 changed files with 8 additions and 5 deletions.
diff --git a/include/boost/graph/detail/adjacency_list.hpp b/include/boost/graph/detail/adjacency_list.hpp
@@ -2228,9 +2228,11 @@ inline typename Config::vertex_descriptor add_vertex(
     vec_adj_list_impl< Graph, Config, Base >& g_)
 {
     Graph& g = static_cast< Graph& >(g_);
-    g.m_vertices.resize(g.m_vertices.size() + 1);
-    g.added_vertex(g.m_vertices.size() - 1);
-    return g.m_vertices.size() - 1;
+    const typename Config::vertex_descriptor added_descriptor
+        = g.m_vertices.size();
+    g.m_vertices.emplace_back();
+    g.added_vertex(added_descriptor);
+    return added_descriptor;
 }
 
 template < class Graph, class Config, class Base >

diff --git a/include/boost/graph/transitive_closure.hpp b/include/boost/graph/transitive_closure.hpp
@@ -151,8 +151,9 @@ void transitive_closure(const Graph& g, GraphTC& tc,
             cg_vertex v = *i;
             if (!in_a_chain[v])
             {
-                chains.resize(chains.size() + 1);
+                chains.push_back(std::vector< cg_vertex >());
                 std::vector< cg_vertex >& chain = chains.back();
+
                 for (;;)
                 {
                     chain.push_back(v);

diff --git a/include/boost/graph/vector_as_graph.hpp b/include/boost/graph/vector_as_graph.hpp
@@ -283,7 +283,7 @@ void remove_edge_if(Predicate p, std::vector< EdgeList, Allocator >& g)
 template < class EdgeList, class Allocator >
 typename EdgeList::value_type add_vertex(std::vector< EdgeList, Allocator >& g)
 {
-    g.resize(g.size() + 1);
+    g.push_back(EdgeList());
     return g.size() - 1;
 }