Java: un poco más inteligente / más rápido
Un poco de código allí. Intento ser más rápido evaluando los empujes en orden de "cuán probable es que esto libere un camino al tesoro", que en sí mismo se basa en dos recorridos de Dijkstra (uno se detiene al encontrar rocas, el otro ignora las rocas). Está funcionando bastante bien, y el único ejemplo del pastebin que parece ser problemático para el autor se resuelve en aproximadamente 2 segundos con esta implementación. Algunos otros ejemplos toman hasta 30-40 segundos, que todavía encuentro demasiado tiempo, pero no pude encontrar una manera de mejorar eso sin romper las cosas :)
He dividido mis cosas en varios archivos para obtener una mejor estructura (también por qué cambié a Ruby desde Java):
Punto de entrada:
import java.util.Date;
public class IndianaJones {
public static void main(final String[] args) throws Exception {
final Maze maze = new Maze(System.in);
final Date startAt = new Date();
final int solution = maze.solve();
final Date endAt = new Date();
System.out.printf("Found solution: %s in %d ms.",
solution < Integer.MAX_VALUE ? solution : "X",
endAt.getTime() - startAt.getTime());
}
}
Direction helper enum:
enum Direction {
UP(-1, 0), DOWN(1, 0), LEFT(0, -1), RIGHT(0, 1);
public final int drow;
public final int dcol;
private Direction(final int drow, final int dcol) {
this.drow = drow;
this.dcol = dcol;
}
public final Direction opposite() {
switch (this) {
case UP:
return DOWN;
case DOWN:
return UP;
case LEFT:
return RIGHT;
case RIGHT:
return LEFT;
}
return null;
}
}
Una clase abstracta para representar una parte ubicada del "laberinto":
abstract class PointOfInterest {
public final int row;
public final int col;
protected PointOfInterest(final int row, final int col) {
this.row = row;
this.col = col;
}
public final boolean isAt(final int row, final int col) {
return this.row == row && this.col == col;
}
@Override
public final String toString() {
return getClass().getSimpleName() + "(" + row + ", " + col + ")";
}
@Override
public final int hashCode() {
return row ^ col;
}
@Override
public final boolean equals(Object obj) {
if (this == obj)
return true;
if (!(obj instanceof PointOfInterest))
return false;
if (!getClass().equals(obj.getClass()))
return false;
final PointOfInterest other = (PointOfInterest) obj;
return row == other.row && col == other.col;
}
}
Y finalmente, el laberinto en sí:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.EnumSet;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;
public class Maze {
private static final char WALL = '1';
private static final char INDY = '2';
private static final char GOAL = '3';
private static final char ROCK = '4';
private final Maze parent;
private final Set<Maze> visited;
private final boolean[][] map;
private final int[][] dijkstra;
private int[][] dijkstraGhost;
private String stringValue = null;
private int shortestSolution = Integer.MAX_VALUE;
private Goal goal = null;
private Indy indy = null;
private Set<Rock> rocks = new HashSet<>();
private Maze(final Maze parent, final Rock rock, final Direction direction) {
this.parent = parent;
this.visited = parent.visited;
map = parent.map;
dijkstra = new int[map.length][map[rock.row].length];
for (final int[] part : dijkstra)
Arrays.fill(part, Integer.MAX_VALUE);
goal = new Goal(parent.goal.row, parent.goal.col);
indy = new Indy(rock.row, rock.col);
for (final Rock r : parent.rocks)
if (r == rock)
rocks.add(new Rock(r.row + direction.drow, r.col + direction.dcol));
else
rocks.add(new Rock(r.row, r.col));
updateDijkstra(goal.row, goal.col, 0, true);
}
public Maze(final InputStream is) {
this.parent = null;
this.visited = new HashSet<>();
try (final BufferedReader br = new BufferedReader(new InputStreamReader(is))) {
String line = br.readLine();
final String[] sizeParts = line.split(" ");
final int height = Integer.parseInt(sizeParts[0]);
final int width = Integer.parseInt(sizeParts[1]);
map = new boolean[height][width];
dijkstra = new int[height][width];
int row = 0;
while ((line = br.readLine()) != null) {
for (int col = 0; col < line.length(); col++) {
final char c = line.charAt(col);
map[row][col] = c == WALL;
dijkstra[row][col] = Integer.MAX_VALUE;
if (c == INDY) {
if (indy != null)
throw new IllegalStateException("Found a second indy!");
indy = new Indy(row, col);
} else if (c == GOAL) {
if (goal != null)
throw new IllegalStateException("Found a second treasure!");
goal = new Goal(row, col);
} else if (c == ROCK) {
rocks.add(new Rock(row, col));
}
}
row++;
}
updateDijkstra(goal.row, goal.col, 0, true);
} catch (final IOException ioe) {
throw new RuntimeException("Could not read maze from InputStream", ioe);
}
}
public int getShortestSolution() {
Maze ptr = this;
while (ptr.parent != null)
ptr = ptr.parent;
return ptr.shortestSolution;
}
public void setShortestSolution(int shortestSolution) {
Maze ptr = this;
while (ptr.parent != null)
ptr = ptr.parent;
ptr.shortestSolution = Math.min(ptr.shortestSolution, shortestSolution);
}
private final boolean isRepeat(final Maze maze) {
return this.visited.contains(maze);
}
private final void updateDijkstra(final int row, final int col, final int value, final boolean force) {
if (row < 0 || col < 0 || row >= dijkstra.length || col >= dijkstra[row].length)
return;
if (map[row][col] || isRockPresent(row, col))
return;
if (dijkstra[row][col] <= value && !force)
return;
dijkstra[row][col] = value;
updateDijkstra(row - 1, col, value + 1, false);
updateDijkstra(row + 1, col, value + 1, false);
updateDijkstra(row, col - 1, value + 1, false);
updateDijkstra(row, col + 1, value + 1, false);
}
private final void updateDijkstraGhost(final int row, final int col, final int value, final boolean force) {
if (row < 0 || col < 0 || row >= dijkstra.length || col >= dijkstra[row].length)
return;
if (map[row][col] || isRockPresent(row, col))
return;
if (dijkstraGhost[row][col] <= value && !force)
return;
dijkstraGhost[row][col] = value;
updateDijkstraGhost(row - 1, col, value + 1, false);
updateDijkstraGhost(row + 1, col, value + 1, false);
updateDijkstraGhost(row, col - 1, value + 1, false);
updateDijkstraGhost(row, col + 1, value + 1, false);
}
private final int dijkstraScore(final int row, final int col) {
if (row < 0 || col < 0 || row >= dijkstra.length || col >= dijkstra[row].length)
return Integer.MAX_VALUE;
return dijkstra[row][col];
}
private final int dijkstraGhostScore(final int row, final int col) {
if (dijkstraGhost == null) {
dijkstraGhost = new int[map.length][map[indy.row].length];
for (final int[] part : dijkstraGhost)
Arrays.fill(part, Integer.MAX_VALUE);
updateDijkstraGhost(goal.row, goal.col, 0, true);
}
if (row < 0 || col < 0 || row >= dijkstra.length || col >= dijkstra[row].length)
return Integer.MAX_VALUE;
return dijkstraGhost[row][col];
}
private boolean isRockPresent(final int row, final int col) {
for (final Rock rock : rocks)
if (rock.isAt(row, col))
return true;
return false;
}
public boolean isEmpty(final int row, final int col) {
if (row < 0 || col < 0 || row >= map.length || col >= map[row].length)
return false;
return !map[row][col] && !isRockPresent(row, col) && !goal.isAt(row, col);
}
public int solve() {
return solve(0);
}
private int solve(final int currentDepth) {
System.out.println(toString());
visited.add(this);
if (isSolved()) {
setShortestSolution(currentDepth);
return 0;
}
if (currentDepth >= getShortestSolution()) {
System.out.println("Aborting at depth " + currentDepth + " because we know better: "
+ getShortestSolution());
return Integer.MAX_VALUE;
}
final Map<Rock, Set<Direction>> nextTries = indy.getMoveableRocks();
int shortest = Integer.MAX_VALUE - 1;
for (final Map.Entry<Rock, Set<Direction>> tries : nextTries.entrySet()) {
final Rock rock = tries.getKey();
for (final Direction dir : tries.getValue()) {
final Maze next = new Maze(this, rock, dir);
if (!isRepeat(next)) {
final int nextSolution = next.solve(currentDepth + 1);
if (nextSolution < shortest)
shortest = nextSolution;
}
}
}
return shortest + 1;
}
public boolean isSolved() {
return indy.canReachTreasure();
}
@Override
public String toString() {
if (stringValue == null) {
final StringBuilder out = new StringBuilder();
for (int row = 0; row < map.length; row++) {
if (row == 0) {
out.append('\u250C');
for (int col = 0; col < map[row].length; col++)
out.append('\u2500');
out.append("\u2510\n");
}
out.append('\u2502');
for (int col = 0; col < map[row].length; col++) {
if (indy.isAt(row, col))
out.append('*');
else if (goal.isAt(row, col))
out.append("$");
else if (isRockPresent(row, col))
out.append("@");
else if (map[row][col])
out.append('\u2588');
else
out.append(base64(dijkstra[row][col]));
}
out.append("\u2502\n");
if (row == map.length - 1) {
out.append('\u2514');
for (int col = 0; col < map[row].length; col++)
out.append('\u2500');
out.append("\u2518\n");
}
}
stringValue = out.toString();
}
return stringValue;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (!obj.getClass().equals(getClass()))
return false;
final Maze other = (Maze) obj;
if (other.map.length != map.length)
return false;
for (int row = 0; row < map.length; row++) {
if (other.map[row].length != map[row].length)
return false;
for (int col = 0; col < map[row].length; col++)
if (other.map[row][col] != map[row][col])
return false;
}
return indy.equals(other.indy) && rocks.equals(other.rocks) && goal.equals(other.goal);
}
@Override
public int hashCode() {
return getClass().hashCode() ^ indy.hashCode() ^ goal.hashCode() ^ rocks.hashCode();
}
private final class Goal extends PointOfInterest {
public Goal(final int row, final int col) {
super(row, col);
}
}
private final class Indy extends PointOfInterest {
public Indy(final int row, final int col) {
super(row, col);
}
public boolean canReachTreasure() {
return dijkstraScore(row, col) < Integer.MAX_VALUE;
}
public SortedMap<Rock, Set<Direction>> getMoveableRocks() {
final SortedMap<Rock, Set<Direction>> out = new TreeMap<>();
@SuppressWarnings("unchecked")
final Set<Direction> checked[][] = new Set[map.length][map[row].length];
lookForRocks(out, checked, row, col, null);
return out;
}
private final void lookForRocks(final Map<Rock, Set<Direction>> rockStore,
final Set<Direction>[][] checked,
final int row,
final int col,
final Direction comingFrom) {
if (row < 0 || col < 0 || row >= checked.length || col >= checked[row].length)
return;
if (checked[row][col] == null)
checked[row][col] = EnumSet.noneOf(Direction.class);
if (checked[row][col].contains(comingFrom))
return;
for (final Rock rock : rocks) {
if (rock.row == row && rock.col == col) {
if (rock.canBeMoved(comingFrom) && rock.isWorthMoving(comingFrom)) {
if (!rockStore.containsKey(rock))
rockStore.put(rock, EnumSet.noneOf(Direction.class));
rockStore.get(rock).add(comingFrom);
}
return;
}
}
if (comingFrom != null)
checked[row][col].add(comingFrom);
for (final Direction dir : Direction.values())
if (comingFrom == null || dir != comingFrom.opposite())
if (isEmpty(row + dir.drow, col + dir.dcol) || isRockPresent(row + dir.drow, col + dir.dcol))
lookForRocks(rockStore, checked, row + dir.drow, col + dir.dcol, dir);
}
}
private final class Rock extends PointOfInterest implements Comparable<Rock> {
public Rock(final int row, final int col) {
super(row, col);
}
public boolean canBeMoved(final Direction direction) {
return isEmpty(row + direction.drow, col + direction.dcol);
}
public boolean isWorthMoving(final Direction direction) {
boolean worthIt = false;
boolean reachable = false;
int emptyAround = 0;
for (final Direction dir : Direction.values()) {
reachable |= (dijkstraScore(row, col) < Integer.MAX_VALUE);
emptyAround += (isEmpty(row + dir.drow, col + dir.dcol) ? 1 : 0);
if (dir != direction && dir != direction.opposite()
&& dijkstraScore(row + dir.drow, col + dir.dcol) < Integer.MAX_VALUE)
worthIt = true;
}
return (emptyAround < 4) && (worthIt || !reachable);
}
public int proximityIndice() {
final int ds = min(dijkstraScore(row - 1, col),
dijkstraScore(row + 1, col),
dijkstraScore(row, col - 1),
dijkstraScore(row, col + 1));
if (ds < Integer.MAX_VALUE)
return ds;
else
return min(dijkstraGhostScore(row - 1, col),
dijkstraGhostScore(row + 1, col),
dijkstraGhostScore(row, col - 1),
dijkstraGhostScore(row, col + 1));
}
@Override
public int compareTo(Rock o) {
return new Integer(proximityIndice()).compareTo(o.proximityIndice());
}
}
private static final char base64(final int i) {
if (i >= 0 && i <= 9)
return (char) ('0' + i);
else if (i < 36)
return (char) ('A' + (i - 10));
else
return ' ';
}
private static final int min(final int i1, final int i2, final int... in) {
int min = Math.min(i1, i2);
for (final int i : in)
min = Math.min(min, i);
return min;
}
}
