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SlidingGame.java
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SlidingGame.java
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package sliding_game;
import java.util.*;
import org.junit.*;
import static org.junit.Assert.*;
public class SlidingGame {
/*
Sliding Game
AirBnB Interview Question
*/
public class Solution {
private final int[][] dirs = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
private int[][] matrix;
private int m;
private int n;
private int originX;
private int originY;
private String recovered;
public Solution(int[][] matrix) {
this.matrix = matrix;
this.m = matrix.length;
this.n = matrix[0].length;
int[][] recoveredMatrix = new int[m][n];
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
if (matrix[i][j] == 0) {
this.originX = i;
this.originY = j;
}
recoveredMatrix[i][j] = i * n + j;
}
}
this.recovered = getMatrixString(recoveredMatrix);
}
public boolean canSolve() {
Queue<int[]> items = new LinkedList<>();
Queue<String> matrix = new LinkedList<>();
Set<String> visited = new HashSet<>();
String stringMatrix = getMatrixString(this.matrix.clone());
items.offer(new int[]{originX, originY});
matrix.offer(stringMatrix);
visited.add(stringMatrix);
while (!items.isEmpty()) {
int size = items.size();
for (int i = 0; i < size; i++) {
int[] curElement = items.poll();
String curMatrixString = matrix.poll();
int x = curElement[0];
int y = curElement[1];
if (curMatrixString.equals(recovered)) {
return true;
}
for (int k = 0; k < dirs.length; k++) {
int xx = x + dirs[k][0];
int yy = y + dirs[k][1];
if (xx < 0 || xx >= m || yy < 0 || yy >= n) {
continue;
}
int[][] newMatrix = recoverMatrixString(curMatrixString);
int temp = newMatrix[x][y];
newMatrix[x][y] = newMatrix[xx][yy];
newMatrix[xx][yy] = temp;
String newMatrixString = getMatrixString(newMatrix);
if (visited.contains(newMatrixString)) {
continue;
}
items.offer(new int[]{xx, yy});
matrix.offer(newMatrixString);
visited.add(newMatrixString);
}
}
}
return false;
}
public List<String> getSolution() {
String[] pathWord = {"Down", "Right", "Up", "Left"};
Queue<int[]> items = new LinkedList<>();
Queue<String> matrix = new LinkedList<>();
Queue<List<String>> path = new LinkedList<>();
Set<String> visited = new HashSet<>();
String stringMatrix = getMatrixString(this.matrix.clone());
items.offer(new int[]{originX, originY});
matrix.offer(stringMatrix);
path.offer(new ArrayList<>());
visited.add(stringMatrix);
while (!items.isEmpty()) {
int size = items.size();
for (int i = 0; i < size; i++) {
int[] curElement = items.poll();
String curMatrixString = matrix.poll();
List<String> curPath = path.poll();
int x = curElement[0];
int y = curElement[1];
if (curMatrixString.equals(recovered)) {
return curPath;
}
for (int k = 0; k < dirs.length; k++) {
int xx = x + dirs[k][0];
int yy = y + dirs[k][1];
if (xx < 0 || xx >= m || yy < 0 || yy >= n) {
continue;
}
int[][] newMatrix = recoverMatrixString(curMatrixString);
int temp = newMatrix[x][y];
newMatrix[x][y] = newMatrix[xx][yy];
newMatrix[xx][yy] = temp;
String newMatrixString = getMatrixString(newMatrix);
if (visited.contains(newMatrixString)) {
continue;
}
List<String> newPath = new ArrayList<>(curPath);
newPath.add(pathWord[k]);
items.offer(new int[]{xx, yy});
matrix.offer(newMatrixString);
path.offer(newPath);
visited.add(newMatrixString);
}
}
}
return new ArrayList<>();
}
private String getMatrixString(int[][] matrix) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
sb.append(matrix[i][j]).append(",");
}
}
return sb.toString();
}
private int[][] recoverMatrixString(String str) {
String[] parts = str.split(",");
int[][] res = new int[m][n];
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
res[i][j] = Integer.parseInt(parts[i * n + j]);
}
}
return res;
}
}
public static class UnitTest {
@Test
public void test1() {
int[][] matrix = {
{3, 1, 4},
{6, 2, 0},
{7, 5, 8}
};
Solution sol = new SlidingGame().new Solution(matrix);
assertTrue(sol.canSolve());
List<String> res = sol.getSolution();
System.out.println(res);
assertEquals(11, (int) res.size());
assertEquals("Left", res.get(0));
assertEquals("Down", res.get(1));
assertEquals("Left", res.get(2));
assertEquals("Up", res.get(3));
assertEquals("Up", res.get(4));
assertEquals("Right", res.get(5));
assertEquals("Right", res.get(6));
assertEquals("Down", res.get(7));
assertEquals("Left", res.get(8));
assertEquals("Up", res.get(9));
assertEquals("Left", res.get(10));
}
}
}