/** 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;
}
}
}
}
}
/**
* Constructs the shortest path array for the given graph.
*
* @param g input graph
* @param <V> a V object.
* @param <E> a E object.
*/
public FloydWarshall(Graph<V, E> g) {
int sz = g.vertexSet().size();
d = new double[sz][sz];
indices = new HashMap<V, Integer>();
// Initialise distance to infinity, or the neighbours weight, or 0 if
// same
for (V v1 : g.vertexSet()) {
for (V v2 : g.vertexSet()) {
if (v1 == v2) {
d[index(v1)][index(v2)] = 0;
} else {
E e = g.getEdge(v1, v2);
if (e == null) {
d[index(v1)][index(v2)] = Double.POSITIVE_INFINITY;
} else {
d[index(v1)][index(v2)] = g.getEdgeWeight(e);
}
}
}
}
// now iterate k times
for (int k = 0; k < sz; k++) {
for (V v1 : g.vertexSet()) {
for (V v2 : g.vertexSet()) {
d[index(v1)][index(v2)] =
Math.min(d[index(v1)][index(v2)], d[index(v1)][k] + d[k][index(v2)]);
if (Double.POSITIVE_INFINITY != d[index(v1)][index(v2)])
diameter = Math.max(diameter, d[index(v1)][index(v2)]);
}
}
}
}
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;
}
