Adding unweighted graph data structure

data_structures/graphs/unweighted_graph.rb

@@ -0,0 +1,62 @@
+require 'set'
+
+##
+# This class aims to represent unweighted graphs
+# (i.e. graphs for which edges between nodes have no specific weight associated to them).
+#
+# Both directed (i.e. an edge between node U and node V does not imply an edge in the opposite direction)
+# and undirected graphs are supported, depending on the constructor invocation.
+
+class UnweightedGraph
+  attr_reader :nodes
+  attr_reader :directed
+
+  def initialize(nodes: [], neighbors: {}, directed: true)
+    @nodes = Set[]
+    @neighbors = {}
+    @directed = directed
+    for node in nodes
+      add_node(node)
+    end
+    neighbors.each do |node, neighbors|
+      for neighbor in neighbors
+        add_edge(node, neighbor)
+      end
+    end
+  end
+
+  def add_node(node)
+    if include?(node)
+      raise ArgumentError, "node #{node} already exists in this graph!"
+    end
+    @nodes.add(node)
+    @neighbors[node] = Set[]
+  end
+
+  def add_edge(start_node, end_node)
+    if has_neighbor?(start_node, end_node)
+      raise ArgumentError, "node #{start_node} already has an edge to #{end_node} in this graph!"
+    end
+    @neighbors[start_node].add(end_node)
+    @neighbors[end_node].add(start_node) unless directed
+  end
+
+  def neighbors(node)
+    unless include?(node)
+      raise ArgumentError, "node #{node} does not exist in this graph!"
+    end
+    @neighbors[node]
+  end
+
+  def empty?
+    nodes.empty?
+  end
+
+  def include?(node)
+    nodes.include?(node)
+  end
+
+  def has_neighbor?(start_node, end_node)
+    neighbors(start_node).include?(end_node)
+  end
+end

data_structures/graphs/unweighted_graph_test.rb

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+require 'minitest/autorun'
+require 'set'
+require_relative 'unweighted_graph'
+
+class TestUnweightedGraph < Minitest::Test
+  def test_directed_unweighted_graph_creation
+    graph = UnweightedGraph.new(nodes: [:u, :v, :w], neighbors: {:u => [:v]}, directed: true)
+
+    assert graph.nodes.to_set == Set[:u, :v, :w]
+    assert graph.neighbors(:u).to_set == Set[:v]
+    assert graph.neighbors(:v).empty?
+    assert graph.neighbors(:w).empty?
+  end
+
+  def test_undirected_unweighted_graph_creation
+    graph = UnweightedGraph.new(nodes: [:u, :v, :w], neighbors: {:u => [:v]}, directed: false)
+
+    assert graph.nodes.to_set == Set[:u, :v, :w]
+    assert graph.neighbors(:u).to_set == Set[:v]
+    assert graph.neighbors(:v).to_set == Set[:u]
+    assert graph.neighbors(:w).empty?
+  end
+
+  def test_empty_returns_true_for_empty_graph
+    graph = UnweightedGraph.new
+
+    assert graph.empty?
+  end
+
+  def test_empty_returns_false_for_non_empty_graph
+    graph = UnweightedGraph.new(nodes: [:u])
+
+    assert !graph.empty?
+  end
+
+  def test_include_returns_true_for_graph_nodes
+    graph = UnweightedGraph.new(nodes: [:u])
+
+    assert graph.include?(:u)
+  end
+
+  def test_include_returns_false_for_non_graph_nodes
+    graph = UnweightedGraph.new
+
+    assert !graph.include?(:u)
+  end
+
+  def test_has_neighbor_returns_true_for_graph_node_neighbors
+    graph = UnweightedGraph.new(nodes: [:u, :v], neighbors: {:u => [:v]})
+
+    assert graph.has_neighbor?(:u, :v)
+  end
+
+  def test_has_neighbor_returns_false_for_non_graph_node_neighbors
+    graph = UnweightedGraph.new(nodes: [:u, :v])
+
+    assert !graph.has_neighbor?(:u, :v)
+  end
+
+  def test_add_node_adds_node_to_graph
+    graph = UnweightedGraph.new
+    graph.add_node(:u)
+
+    assert graph.nodes.to_set == Set[:u]
+  end
+
+  def test_add_edge_adds_edge_to_directed_unweighted_graph
+    graph = UnweightedGraph.new(nodes: [:u, :v], directed: true)
+    graph.add_edge(:u, :v)
+
+    assert graph.neighbors(:u).to_set == Set[:v]
+    assert graph.neighbors(:v).empty?
+  end
+
+  def test_add_edge_adds_edge_to_directed_unweighted_graph
+    graph = UnweightedGraph.new(nodes: [:u, :v], directed: false)
+    graph.add_edge(:u, :v)
+
+    assert graph.neighbors(:u).to_set == Set[:v]
+    assert graph.neighbors(:v).to_set == Set[:u]
+  end
+end