/** Calculate the shortest paths (not done per default) */
private void lazyCalculatePaths() {
// already we have calculated it once.
if (paths != null) {
return;
}
lazyCalculateMatrix();
Map<VertexPair<V>, GraphPath<V, E>> sps = new HashMap<VertexPair<V>, GraphPath<V, E>>();
int n = vertices.size();
nShortestPaths = 0;
for (int i = 0; i < n; i++) {
V v_i = vertices.get(i);
for (int j = 0; j < n; j++) {
// don't count this.
if (i == j) {
continue;
}
V v_j = vertices.get(j);
GraphPath<V, E> path = getShortestPathImpl(v_i, v_j);
// we got a path
if (path != null) {
sps.put(new VertexPair<V>(v_i, v_j), path);
nShortestPaths++;
}
}
}
this.paths = sps;
}
/**
* @return the diameter (longest of all the shortest paths) computed for the graph. If the graph
* is vertexless, return 0.0.
*/
public double getDiameter() {
lazyCalculateMatrix();
if (Double.isNaN(diameter)) {
diameter = 0.0;
int n = vertices.size();
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (!Double.isInfinite(d[i][j]) && d[i][j] > diameter) {
diameter = d[i][j];
}
}
}
}
return diameter;
}
/**
* Get the length of a shortest path.
*
* @param a first vertex
* @param b second vertex
* @return shortest distance between a and b
*/
public double shortestDistance(V a, V b) {
lazyCalculateMatrix();
return d[vertices.indexOf(a)][vertices.indexOf(b)];
}