Adding node consumer support on graph BFS

data_structures/graphs/bfs.rb

@@ -25,12 +25,13 @@ end
 ##
 # Performs a breadth-first search for the provided graph, starting at the given node.
 # Returns the search result (see GraphBfsResult).
+# Nodes are consumed upon discovery using the provided node consumer (nothing, by default).
 #
 # The algorithm has a time complexity of O(|V| + |E|), where:
 # - |V| is the number of nodes in the graph;
 # - |E| is the number of edges in the graph.
 
-def bfs(graph, start_node)
+def bfs(graph, start_node, node_consumer=method(:do_nothing_on_node))
   seen = Set[]
   visited = Set[]
   parents = { start_node => nil }
@@ -41,6 +42,7 @@ def bfs(graph, start_node)
   q.push(start_node)
   until q.empty?
     node = q.pop
+    node_consumer.call(node)
     for neighbor in graph.neighbors(node)
       unless seen.include?(neighbor)
         seen.add(neighbor)
@@ -54,3 +56,7 @@ def bfs(graph, start_node)
 
   GraphBfsResult.new(visited, parents, distances)
 end
+
+private
+def do_nothing_on_node(node)
+end

data_structures/graphs/bfs_test.rb

@@ -18,7 +18,7 @@ class TestBfs < Minitest::Test
     }
   end
 
-  def test_bfs_visits_undirected_graph_fully
+  def test_bfs_visits_graph_fully
     graph = UnweightedGraph.new(nodes: [:u, :v, :w, :x], directed: false)
     graph.add_edge(:u, :v)
     graph.add_edge(:u, :w)
@@ -41,7 +41,7 @@ class TestBfs < Minitest::Test
     }
   end
 
-  def test_bfs_visits_undirected_graph_partially
+  def test_bfs_visits_graph_partially
     graph = UnweightedGraph.new(nodes: [:u, :v, :w, :x, :y, :z], directed: false)
     graph.add_edge(:u, :v)
     graph.add_edge(:w, :x)
@@ -64,4 +64,15 @@ class TestBfs < Minitest::Test
       :z => 2
     }
   end
+
+  def test_bfs_visits_with_node_consumer
+    graph = UnweightedGraph.new(nodes: [:u, :v, :w], directed: false)
+    graph.add_edge(:u, :v)
+    graph.add_edge(:u, :w)
+
+    visit_order = []
+    bfs(graph, :w, ->(node) { visit_order.append(node) })
+
+    assert visit_order == [:w, :u, :v]
+  end
 end