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/* vim: set expandtab tabstop=4 shiftwidth=4 : */
import java.util.Iterator;
public class SAP
{
private final Digraph g;
private final BFS vBFS;
private final BFS wBFS;
private class BFS implements Iterable<Integer>
{
private static final int MAXINT = Integer.MAX_VALUE;
private boolean[] marked;
private int[] distTo;
private Queue<Integer> visited;
private Queue<Integer> q;
public BFS(int size)
{
marked = new boolean[size];
distTo = new int[size];
visited = new Queue<Integer>();
q = new Queue<Integer>();
for (int v = 0; v < size; v++) {
// distTo[v] = -1;
marked[v] = false;
}
}
public void bfs(int s)
{
clear();
marked[s] = true;
distTo[s] = 0;
q.enqueue(s);
visited.enqueue(s);
bfs();
}
public void bfs(Iterable<Integer> ss)
{
clear();
for (int s : ss) {
marked[s] = true;
distTo[s] = 0;
q.enqueue(s);
visited.enqueue(s);
}
bfs();
}
public int distTo(int v)
{
return distTo[v];
}
public boolean hasPathTo(int v)
{
return marked[v];
}
public Iterator<Integer> iterator() {
return visited.iterator();
}
public int visitedCount()
{
return visited.size();
}
private void clear()
{
while (!visited.isEmpty()) {
marked[visited.dequeue()] = false;
}
}
private void bfs()
{
while (!q.isEmpty()) {
int v = q.dequeue();
for (int w : g.adj(v)) {
if (!marked[w]) {
distTo[w] = distTo[v] + 1;
marked[w] = true;
q.enqueue(w);
visited.enqueue(w);
}
}
}
}
}
// data type use space proportional to E + V
// all methods take time at most proportional to E + V in the worst case
// constructor takes a digraph (not necessarily a DAG)
public SAP(Digraph G)
{
g = new Digraph(G);
vBFS = new BFS(G.V());
wBFS = new BFS(G.V());
}
// length of shortest ancestral path between v and w
// -1 if no such path
public int length(int v, int w)
{
check(v);
check(w);
vBFS.bfs(v);
wBFS.bfs(w);
return distance();
}
// a common ancestor of v and w that participates in a shortest ancestral path
// -1 if no such path
public int ancestor(int v, int w)
{
check(v);
check(w);
vBFS.bfs(v);
wBFS.bfs(w);
return ancestor();
}
// length of shortest ancestral path between any vertex in v and any vertex in w
// -1 if no such path
public int length(Iterable<Integer> v, Iterable<Integer> w)
{
check(v);
check(w);
vBFS.bfs(v);
wBFS.bfs(w);
return distance();
}
// a common ancestor that participates in shortest ancestral path
// -1 if no such path
public int ancestor(Iterable<Integer> v, Iterable<Integer> w)
{
check(v);
check(w);
vBFS.bfs(v);
wBFS.bfs(w);
return ancestor();
}
private int distance()
{
BFS aBFS, bBFS;
if (vBFS.visitedCount() < wBFS.visitedCount()) {
aBFS = vBFS;
bBFS = wBFS;
} else {
aBFS = wBFS;
bBFS = vBFS;
}
int len = Integer.MAX_VALUE;
for (int x : aBFS) {
if (bBFS.hasPathTo(x)) {
int l = aBFS.distTo(x) + bBFS.distTo(x);
if (l < len) {
len = l;
}
}
}
if (len == Integer.MAX_VALUE)
return -1;
return len;
}
private int ancestor()
{
BFS aBFS, bBFS;
if (vBFS.visitedCount() < wBFS.visitedCount()) {
aBFS = vBFS;
bBFS = wBFS;
} else {
aBFS = wBFS;
bBFS = vBFS;
}
int ancestor = -1;
int len = Integer.MAX_VALUE;
for (int x : aBFS) {
if (bBFS.hasPathTo(x)) {
int l = aBFS.distTo(x) + bBFS.distTo(x);
if (l < len) {
len = l;
ancestor = x;
}
}
}
return ancestor;
}
private void check(int v)
{
if (v < 0 || v >= g.V())
throw new IndexOutOfBoundsException("out of index");
}
private void check(Iterable<Integer> vs)
{
for (int v : vs) {
check(v);
}
}
// for unit testing of this class (such as the one below)
public static void main(String[] args)
{
int length, ancestor;
In in;
Digraph G;
SAP sap;
in = new In("./data/digraph1.txt");
G = new Digraph(in);
sap = new SAP(G);
length = sap.length(3, 11);
ancestor = sap.ancestor(3, 11);
StdOut.printf("length = %d, ancestor = %d\n", length, ancestor);
length = sap.length(9, 12);
ancestor = sap.ancestor(9, 12);
StdOut.printf("length = %d, ancestor = %d\n", length, ancestor);
length = sap.length(7, 2);
ancestor = sap.ancestor(7, 2);
StdOut.printf("length = %d, ancestor = %d\n", length, ancestor);
length = sap.length(1, 6);
ancestor = sap.ancestor(1, 6);
StdOut.printf("length = %d, ancestor = %d\n", length, ancestor);
Stopwatch w1 = new Stopwatch();
for (int i = 1; i < 7; i++) {
String g = "./data/digraph"+i+".txt";
in = new In(g);
G = new Digraph(in);
sap = new SAP(G);
for (int v = 0; v < G.V(); v++) {
for (int w = 0; w < G.V(); w++) {
int a = sap.ancestor(v, w);
int l = sap.length(v, w);
// StdOut.printf("%s %d->%d : a:%d l:%d\n", g, v, w, a, l);
}
}
}
double a1 = w1.elapsedTime();
StdOut.printf("all solved in : %g \n", a1);
}
}
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