*/
  public static <N> Graph<N> transpose(Graph<N> graph) {
    if (!graph.isDirected()) {
      return graph; // the transpose of an undirected graph is an identical graph
    }

    if (graph instanceof TransposedGraph) {
      return ((TransposedGraph<N>) graph).graph;
    }

    return new TransposedGraph<>(graph);
  }

  /**

 */

package com.google.common.graph;

import static com.google.common.graph.Graphs.hasCycle;
import static com.google.common.truth.Truth.assertThat;

import com.google.common.collect.ImmutableList;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/** Tests for {@link Graphs#hasCycle(Graph)} and {@link Graphs#hasCycle(Network)}. */

 */

package com.google.common.graph;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.graph.GraphConstants.DEFAULT_EDGE_COUNT;
import static com.google.common.graph.GraphConstants.DEFAULT_NODE_COUNT;
import static com.google.common.graph.GraphConstants.EDGE_NOT_IN_GRAPH;

 * limitations under the License.
 */

package com.google.common.graph;

import static com.google.common.graph.Graphs.copyOf;
import static com.google.common.graph.Graphs.inducedSubgraph;
import static com.google.common.graph.Graphs.reachableNodes;
import static com.google.common.graph.Graphs.transitiveClosure;
import static com.google.common.graph.Graphs.transpose;
import static com.google.common.truth.Truth.assertThat;

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.graph;

import com.google.common.base.Optional;

/**
 * A base class for builders that construct graphs with user-defined properties.
 *
 * @author James Sexton
 */
@ElementTypesAreNonnullByDefault
abstract class AbstractGraphBuilder<N> {
  final boolean directed;

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.graph;

import com.google.common.graph.GraphConstants.Presence;

/**
 * Standard implementation of {@link MutableGraph} that supports both directed and undirected
 * graphs. Instances of this class should be constructed with {@link GraphBuilder}.
 *

  MutableValueGraph<Integer, String> graph;

  @After
  public void validateGraphState() {
    assertStronglyEquivalent(graph, Graphs.copyOf(graph));
    assertStronglyEquivalent(graph, ImmutableValueGraph.copyOf(graph));

    Graph<Integer> asGraph = graph.asGraph();
    AbstractGraphTest.validateGraph(asGraph);
    assertThat(graph.nodes()).isEqualTo(asGraph.nodes());
    assertThat(graph.edges()).isEqualTo(asGraph.edges());

        assertThat(graph.predecessors(node)).hasSize(graph.inDegree(node));
        assertThat(graph.successors(node)).hasSize(graph.outDegree(node));
      } else {
        int selfLoopCount = graph.adjacentNodes(node).contains(node) ? 1 : 0;
        assertThat(graph.degree(node)).isEqualTo(graph.adjacentNodes(node).size() + selfLoopCount);

      MutableGraph<Integer> graph = graphBuilder.allowsSelfLoops(true).build();

      assertThat(graph.nodes()).isEmpty();
      assertThat(graph.edges()).isEmpty();
      AbstractGraphTest.validateGraph(graph);

      while (graph.nodes().size() < NUM_NODES) {
        graph.addNode(gen.nextInt(NODE_POOL_SIZE));
      }
      ArrayList<Integer> nodeList = new ArrayList<>(graph.nodes());

  // Error messages
  static final String NODE_NOT_IN_GRAPH = "Node %s is not an element of this graph.";
  static final String EDGE_NOT_IN_GRAPH = "Edge %s is not an element of this graph.";
  static final String NODE_REMOVED_FROM_GRAPH =
      "Node %s that was used to generate this set is no longer in the graph.";
  static final String NODE_PAIR_REMOVED_FROM_GRAPH =