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/* vim: set expandtab tabstop=4 shiftwidth=4 : */
import java.util.Iterator;
// import java.util.Collection;
// import java.util.ArrayDeque;
public class Solver
{
private SearchNode sol0;
private SearchNode sol1;
private final MinPQ<SearchNode> pq0;
private final MinPQ<SearchNode> pq1;
private final RedBlackBST<String, Board> gameTree0;
private final RedBlackBST<String, Board> gameTree1;
private class SearchNode implements Comparable<SearchNode>
{
private final int moves;
private final int fitness;
private final SearchNode parent;
private final Board board;
private final String key;
public SearchNode(Board b, SearchNode p, int n)
{
this.board = b;
this.parent = p;
this.moves = n;
// this.fitness = n + b.hamming();
this.fitness = n + b.manhattan();
this.key = b.toString().replace(" ", "").replace("\n", "");
}
public String getKey() { return key; }
public int getFitness() { return fitness; }
public int getMoves() { return moves; }
public Board getBoard() { return board; }
public SearchNode getParent() { return parent; }
public int compareTo(SearchNode that)
{
if (this == that) return 0;
if (this.fitness > that.fitness) return 1;
else if (this.fitness < that.fitness) return -1;
else return 0;
}
}
private class SearchNodeIterator implements Iterator<SearchNode> {
private SearchNode current;
public SearchNodeIterator(SearchNode n) {
current = n;
}
public boolean hasNext() { return current.getParent() != null; }
public void remove() { throw new UnsupportedOperationException(); }
public SearchNode next() {
if (!hasNext()) throw new java.util.NoSuchElementException();
return current.getParent();
}
}
// find a solution to the initial board (using the A* algorithm)
public Solver(Board initial)
{
sol0 = null;
sol1 = null;
pq0 = new MinPQ<SearchNode>();
pq1 = new MinPQ<SearchNode>();
gameTree0 = new RedBlackBST<String, Board>();
gameTree1 = new RedBlackBST<String, Board>();
pq0.insert(new SearchNode(initial, null, 0));
pq1.insert(new SearchNode(initial.twin(), null, 0));
solve();
}
private boolean isKnown(SearchNode n, Board b)
{
SearchNode p = n.getParent();
while (p != null)
{
if (b.equals(p.getBoard())) return true;
p = p.getParent();
}
return false;
}
private void solve()
{
while ((sol0 == null) && (sol1 == null))
{
if (pq0.isEmpty() && pq1.isEmpty())
{
// StdOut.println("FAIL");
break;
}
if (!pq0.isEmpty())
{
SearchNode n = pq0.delMin();
Board b = n.getBoard();
if (b.isGoal())
{
sol0 = n;
break;
}
if (gameTree0.contains(n.getKey()))
continue;
int m = n.getMoves() + 1;
SearchNode p = n.getParent();
if (p == null) {
for (Board nb : b.neighbors())
pq0.insert(new SearchNode(nb, n, m));
}
else {
Board pb = p.getBoard();
for (Board nb : b.neighbors())
{
if (!pb.equals(nb))
pq0.insert(new SearchNode(nb, n, m));
}
}
gameTree0.put(n.getKey(), b);
}
if (!pq1.isEmpty())
{
SearchNode n = pq1.delMin();
Board b = n.getBoard();
if (b.isGoal())
{
sol1 = n;
break;
}
if (gameTree1.contains(n.getKey()))
continue;
int m = n.getMoves() + 1;
SearchNode p = n.getParent();
if (p == null) {
for (Board nb : b.neighbors())
pq1.insert(new SearchNode(nb, n, m));
}
else {
Board pb = p.getBoard();
for (Board nb : b.neighbors())
{
if (!pb.equals(nb))
pq1.insert(new SearchNode(nb, n, m));
}
}
gameTree1.put(n.getKey(), b);
}
}
}
// is the initial board solvable?
public boolean isSolvable()
{
return (sol0 != null);
}
// min number of moves to solve initial board; -1 if no solution
public int moves()
{
if (!isSolvable()) return -1;
return sol0.getMoves();
}
// sequence of boards in a shortest solution; null if no solution
public Iterable<Board> solution()
{
if (!isSolvable()) return null;
Stack<Board> s = new Stack<Board>();
SearchNode n = sol0;
while (n != null)
{
s.push(n.getBoard());
n = n.getParent();
}
return s;
}
// solve a slider puzzle (given below)
public static void main(String[] args)
{
// Stopwatch w = new Stopwatch();
// create initial board from file
In in = new In(args[0]);
int N = in.readInt();
int[][] blocks = new int[N][N];
for (int i = 0; i < N; i++)
for (int j = 0; j < N; j++)
blocks[i][j] = in.readInt();
Board initial = new Board(blocks);
// solve the puzzle
Solver solver = new Solver(initial);
// print solution to standard output
if (!solver.isSolvable())
StdOut.println("No solution possible");
else {
StdOut.println("Minimum number of moves = " + solver.moves()+"\n");
for (Board board : solver.solution())
StdOut.println(board);
}
// StdOut.printf("Time: %f\n\n", w.elapsedTime());
}
}
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