Method transitiveClosure

guava/src/com/google/common/graph/Graphs.java:190–203

(
      Graph<N> graph, TransitiveClosureSelfLoopStrategy strategy)

   */
  // TODO(b/31438252): Consider optimizing for undirected graphs.
  public static <N> ImmutableGraph<N> transitiveClosure(
      Graph<N> graph, TransitiveClosureSelfLoopStrategy strategy) {
    ImmutableGraph.Builder<N> transitiveClosure =
        GraphBuilder.from(graph).allowsSelfLoops(true).<N>immutable();

    for (N node : graph.nodes()) {
      // add each node explicitly to include isolated nodes
      transitiveClosure.addNode(node);
      for (N reachableNode : getReachableNodes(graph, node, strategy)) {
        transitiveClosure.putEdge(node, reachableNode);
      }
    }
    return transitiveClosure.build();
  }

  /**
   * Equivalent to {@code transitiveClosure(graph, ADD_SELF_LOOPS_ALWAYS)}. Callers should look at