/**
* TODO
*
* @param graph
* @param edge
*/
private void refreshGraph(ArrayList<ArrayList<Integer>> graph, SimpleEdge edge) {
int v = edge.getBeginVertix();
int u = edge.getEndVertix();
for (ArrayList<Integer> vertices : graph) {
for (int vertix = 1; vertix < vertices.size(); vertix++) {
if (vertices.get(vertix) == u) {
vertices.set(vertix, v);
}
}
}
}
/**
* TODO
*
* @param graph
* @param edge
*/
public void mergeTwoVertices(ArrayList<ArrayList<Integer>> graph, SimpleEdge edge) {
int v = edge.getBeginVertix();
int u = edge.getEndVertix();
ArrayList<Integer> vv = graph.get(v);
ArrayList<Integer> uu = graph.get(u);
ArrayList<Integer> rr = new ArrayList<Integer>();
// TODO
rr.add(vv.get(0));
mergingVertexLists(rr, vv, vv.get(0), uu.get(0));
mergingVertexLists(rr, uu, vv.get(0), uu.get(0));
graph.set(v, rr);
graph.remove(u);
}
/**
* @param graph
* @return
*/
public SimpleEdge pickRandomEdge(ArrayList<ArrayList<Integer>> graph) {
SimpleEdge edge = new SimpleEdge();
int max = graph.size();
int beginRandomIndex = AlgoHelper.randomNumber(0, max);
ArrayList<Integer> t = graph.get(beginRandomIndex);
int randomVertix = AlgoHelper.randomNumber(1, t.size());
int randomIndex = findEndIndex(graph, t.get(randomVertix));
if (beginRandomIndex < randomIndex) {
edge.setBeginVertix(beginRandomIndex);
edge.setEndVertix(randomIndex);
} else {
edge.setBeginVertix(randomIndex);
edge.setEndVertix(beginRandomIndex);
}
return edge;
}
/**
* karger's min cut algorithm
*
* <p>While there are more than 2 vertices: • pick a remaining edge (u,v) uniformly at random •
* merge (or “contract” ) u and v into a single vertex • remove self-loops return cut represented
* by final 2 vertices. 8
*
* @param graph graph represented as adjacenty list
* @return computed minCut value
*/
public long kargerMinCutAlgo(ArrayList<ArrayList<Integer>> graph) {
int numberOfVertices = graph.size();
// verticiesIndex - vertex's(ArrayList<Integer>) index in graph arrayList
SimpleEdge verticiesIndex = null;
// verticiesLabel - vertex label (the first integer value in ArrayList<Integer>)
SimpleEdge verticiesLabel = new SimpleEdge();
while (numberOfVertices != 2) {
verticiesIndex = pickRandomEdge(graph);
verticiesLabel.setBeginVertix(graph.get(verticiesIndex.getBeginVertix()).get(0));
verticiesLabel.setEndVertix(graph.get(verticiesIndex.getEndVertix()).get(0));
mergeTwoVertices(graph, verticiesIndex);
refreshGraph(graph, verticiesLabel);
numberOfVertices--;
}
return graph.get(0).size() - 1;
}
