findLCA = function findLCA(node1, node2, layoutInfo) {
  // Find their common ancester, starting from the root graph
  var res = findLCA_aux(node1, node2, 0, layoutInfo);

  if (2 > res.count) {
    // If aux function couldn't find the common ancester,
    // then it is the root graph
    return 0;
  } else {
    return res.graph;
  }
}
@brief : This function finds the index of the lowest common
         graph ancestor between 2 nodes in the subtree
         (from the graph hierarchy induced tree) whose
         root is graphIx

@arg node1: node1's ID
@arg node2: node2's ID
@arg layoutInfo: layoutInfo object