/** Introduces the necessary shortcuts for endNode v in the graph. */
int addShortcuts(int v) {
shortcuts.clear();
findShortcuts(addScHandler.setNode(v));
int tmpNewShortcuts = 0;
for (Shortcut sc : shortcuts.keySet()) {
boolean updatedInGraph = false;
// check if we need to update some existing shortcut in the graph
EdgeSkipIterator iter = vehicleOutExplorer.setBaseNode(sc.from);
while (iter.next()) {
if (iter.isShortcut()
&& iter.getAdjNode() == sc.to
&& prepareEncoder.canBeOverwritten(iter.getFlags(), sc.flags)
&& iter.getDistance() > sc.weight) {
iter.setFlags(sc.flags);
iter.setSkippedEdges(sc.skippedEdge1, sc.skippedEdge2);
iter.setDistance(sc.weight);
setOrigEdgeCount(iter.getEdge(), sc.originalEdges);
updatedInGraph = true;
break;
}
}
if (!updatedInGraph) {
EdgeSkipIterState edgeState = g.shortcut(sc.from, sc.to);
edgeState.setDistance(sc.weight).setFlags(sc.flags);
edgeState.setSkippedEdges(sc.skippedEdge1, sc.skippedEdge2);
setOrigEdgeCount(edgeState.getEdge(), sc.originalEdges);
tmpNewShortcuts++;
}
}
return tmpNewShortcuts;
}
/**
* Calculates the priority of endNode v without changing the graph. Warning: the calculated
* priority must NOT depend on priority(v) and therefor findShortcuts should also not depend on
* the priority(v). Otherwise updating the priority before contracting in contractNodes() could
* lead to a slowishor even endless loop.
*/
int calculatePriority(int v) {
// set of shortcuts that would be added if endNode v would be contracted next.
findShortcuts(calcScHandler.setNode(v));
// System.out.println(v + "\t " + tmpShortcuts);
// # huge influence: the bigger the less shortcuts gets created and the faster is the
// preparation
//
// every endNode has an 'original edge' number associated. initially it is r=1
// when a new shortcut is introduced then r of the associated edges is summed up:
// r(u,w)=r(u,v)+r(v,w) now we can define
// originalEdgesCount = σ(v) := sum_{ (u,w) ∈ shortcuts(v) } of r(u, w)
int originalEdgesCount = calcScHandler.originalEdgesCount;
// for (Shortcut sc : tmpShortcuts) {
// originalEdgesCount += sc.originalEdges;
// }
// # lowest influence on preparation speed or shortcut creation count
// (but according to paper should speed up queries)
//
// number of already contracted neighbors of v
int contractedNeighbors = 0;
int degree = 0;
EdgeSkipIterator iter = calcPrioAllExplorer.setBaseNode(v);
while (iter.next()) {
degree++;
if (iter.isShortcut()) contractedNeighbors++;
}
// from shortcuts we can compute the edgeDifference
// # low influence: with it the shortcut creation is slightly faster
//
// |shortcuts(v)| − |{(u, v) | v uncontracted}| − |{(v, w) | v uncontracted}|
// meanDegree is used instead of outDegree+inDegree as if one endNode is in both directions
// only one bucket memory is used. Additionally one shortcut could also stand for two
// directions.
int edgeDifference = calcScHandler.shortcuts - degree;
// according to the paper do a simple linear combination of the properties to get the priority.
// this is the current optimum for unterfranken:
return 10 * edgeDifference + originalEdgesCount + contractedNeighbors;
}