/** Calculates the matrix of all shortest paths, but does not populate the paths map. */
private void lazyCalculateMatrix() {
if (d != null) {
// already done
return;
}
int n = vertices.size();
// init the backtrace matrix
backtrace = new int[n][n];
for (int i = 0; i < n; i++) {
Arrays.fill(backtrace[i], -1);
}
// initialize matrix, 0
d = new double[n][n];
for (int i = 0; i < n; i++) {
Arrays.fill(d[i], Double.POSITIVE_INFINITY);
}
// initialize matrix, 1
for (int i = 0; i < n; i++) {
d[i][i] = 0.0;
}
// initialize matrix, 2
Set<E> edges = graph.edgeSet();
for (E edge : edges) {
V v1 = graph.getEdgeSource(edge);
V v2 = graph.getEdgeTarget(edge);
int v_1 = vertices.indexOf(v1);
int v_2 = vertices.indexOf(v2);
d[v_1][v_2] = graph.getEdgeWeight(edge);
if (!(graph instanceof DirectedGraph<?, ?>)) {
d[v_2][v_1] = graph.getEdgeWeight(edge);
}
}
// run fw alg
for (int k = 0; k < n; k++) {
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
double ik_kj = d[i][k] + d[k][j];
if (ik_kj < d[i][j]) {
d[i][j] = ik_kj;
backtrace[i][j] = k;
}
}
}
}
}
private void shortestPathRecur(List<E> edges, int v_a, int v_b) {
int k = backtrace[v_a][v_b];
if (k == -1) {
E edge = graph.getEdge(vertices.get(v_a), vertices.get(v_b));
if (edge != null) {
edges.add(edge);
}
} else {
shortestPathRecur(edges, v_a, k);
shortestPathRecur(edges, k, v_b);
}
}
private GraphPath<V, E> getShortestPathImpl(V a, V b) {
int v_a = vertices.indexOf(a);
int v_b = vertices.indexOf(b);
List<E> edges = new ArrayList<E>();
shortestPathRecur(edges, v_a, v_b);
// no path, return null
if (edges.size() < 1) {
return null;
}
double weight = 0.;
for (E e : edges) {
weight += graph.getEdgeWeight(e);
}
GraphPathImpl<V, E> path = new GraphPathImpl<V, E>(graph, a, b, edges, weight);
return path;
}
public FloydWarshallShortestPaths(Graph<V, E> graph) {
this.graph = graph;
this.vertices = new ArrayList<V>(graph.vertexSet());
}