getSubgraphAdjacencyList(vertexIds) {
    let length = vertexIds.length;
    let adjacencyList = Array(length);

    for (var i = 0; i < length; i++) {
      adjacencyList[i] = Array();

      for (var j = 0; j < length; j++) {
        if (i === j) {
          continue;
        }

        if (this.hasEdge(vertexIds[i], vertexIds[j])) {
          adjacencyList[i].push(j);
        }
      }
    }

    return adjacencyList;
  }
Get the adjacency list of a subgraph.

@param {Number[]} vertexIds An array containing the vertex ids contained within the subgraph.
@returns {Array[]} The adjancency list of the subgraph.