import static java.util.Objects.requireNonNull;

import com.google.common.collect.ImmutableList;
import com.google.errorprone.annotations.CanIgnoreReturnValue;

/**
 * Standard implementation of {@link MutableNetwork} that supports both directed and undirected
 * graphs. Instances of this class should be constructed with {@link NetworkBuilder}.
 *
 * <p>Time complexities for mutation methods are all O(1) except for {@code removeNode(N node)},

    this.allowsSelfLoops = allowsSelfLoops;
    this.allowsParallelEdges = allowsParallelEdges;
    this.nodeOrder = nodeOrder;
    this.edgeOrder = edgeOrder;
  }

  @Override
  MutableNetwork<Integer, String> createGraph() {
    return NetworkBuilder.directed()
        .allowsSelfLoops(allowsSelfLoops)
        .allowsParallelEdges(allowsParallelEdges)
        .nodeOrder(nodeOrder)
        .edgeOrder(edgeOrder)

    this.allowsSelfLoops = allowsSelfLoops;
    this.allowsParallelEdges = allowsParallelEdges;
    this.nodeOrder = nodeOrder;
    this.edgeOrder = edgeOrder;
  }

  @Override
  MutableNetwork<Integer, String> createGraph() {
    return NetworkBuilder.undirected()
        .allowsSelfLoops(allowsSelfLoops)
        .allowsParallelEdges(allowsParallelEdges)
        .nodeOrder(nodeOrder)

    this.allowsSelfLoops = allowsSelfLoops;
    this.allowsParallelEdges = allowsParallelEdges;
    this.nodeOrder = nodeOrder;
    this.edgeOrder = edgeOrder;
  }

  @Override
  MutableNetwork<Integer, String> createGraph() {
    return NetworkBuilder.directed()
        .allowsSelfLoops(allowsSelfLoops)
        .allowsParallelEdges(allowsParallelEdges)
        .nodeOrder(nodeOrder)
        .edgeOrder(edgeOrder)

    Random gen = new Random(42); // Fixed seed so test results are deterministic.

    for (int trial = 0; trial < NUM_TRIALS; ++trial) {
      MutableNetwork<Integer, Object> network =
          networkBuilder.allowsParallelEdges(true).allowsSelfLoops(true).build();

      assertThat(network.nodes()).isEmpty();
      assertThat(network.edges()).isEmpty();

 * create an instance of one of the built-in implementations of {@code Network}, use the {@link
 * NetworkBuilder} class:
 *
 * {@snippet :
 * MutableNetwork<Integer, MyEdge> network = NetworkBuilder.directed().build();
 * }
 *
 * <p>{@link NetworkBuilder#build()} returns an instance of {@link MutableNetwork}, which is a
 * subtype of {@code Network} that provides methods for adding and removing nodes and edges. If you

  public void forTree_acceptsDirectedNetwork() throws Exception {
    MutableNetwork<String, Integer> network = NetworkBuilder.directed().build();
    network.addEdge("a", "b", 11);

    Traverser.forTree(network); // Does not throw
  }

  @Test
  public void forTree_withUndirectedNetwork_throws() throws Exception {
    MutableNetwork<String, Integer> network = NetworkBuilder.undirected().build();