Implemented function
  • Shuffle
  • Slide
  • Solve the game using backtracking (sometimes will fail/unable to solve)

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package airbnb;
import java.util.Random;

public class TileBoard {
 int[][] board;
 int[][] visited;
 int x;
 int y;
 
 public TileBoard() {
  board = new int[3][3];
  int start = 1;
  for (int i = 0; i < 3; i++) {
   for (int j = 0; j < 3; j++) {
    if (start >= 9) {
     break;
    }
    board[i][j] = start++;
   }
  }
  x = 2;
  y = 2;
  visited = new int[3][3];
 }
 
 public void shuffle() {
  Random random = new Random();
  int moves = random.nextInt(5);
  while (moves > 0) {
   int dir = random.nextInt(4);
   try {
    slide(Direction.values()[dir], 0, false);
    moves--;
   } catch (RuntimeException e) {
    
   }
  }
  System.out.println("finished shuffle");
 }
 
 public boolean sovle() {
  return solveHelper(1, 0);
 }
 
 
 public boolean solveHelper(int level, int moves) {
  if (x == 2 && y == 2) {
   if (moves == 1) {
    System.out.println("back to 2,2");
   }
   return finalCheck();
  } else if (moves >= 8) { // seems unnecessary
   return false;
  } else {
   int oldX = x;
   int oldY = y;
   for (Direction dir : Direction.values()) {
    visited[oldX][oldY] = 1;
    try {
     slide(dir, level, false);
     System.out.println(toString());
    } catch (RuntimeException e) {
     continue;
    }
    if (solveHelper(level + 1, moves + 1)) {
     return true;
    } else {
     try {
      Direction back = reverse(dir);
      System.out.println("reversing " + back.toString());
      slide(back, level, true);
      System.out.println(toString());
     } catch (RuntimeException e) {
      
     }
    }
   }
   return false;
  }
 }
 
 public Direction reverse(Direction dir) {
  switch (dir) {
   case Up:
    return Direction.down;
   case down:
    return Direction.Up;
   case left:
    return Direction.right;
   case right:
    return Direction.left;
  }
  return null;
 }
 
 public boolean finalCheck() {
  int start = 1;
  for (int i = 0; i < 3; i++) {
   for (int j = 0; j < 3; j++) {
    if (start > 8) {
     break;
    }
    if (board[i][j] != start++) {
     return false;
    } 
   }
  }
  return true;
 }
 public void slide(Direction direction, int level, boolean reverse) {
  int newY = y;
  int newX = x;
  switch (direction) {
  case Up:
   newX = x - 1;
   if (newX < 0) {
    throw new RuntimeException();
   }
   break;
  case down:
   newX = x + 1;
   if (newX > 2) {
    throw new RuntimeException();
   }
   break;
  case left:
   newY = y - 1;
   if (newY < 0) {
    throw new RuntimeException();
   }
   break;
  case right:
   newY = y + 1;
   if (newY > 2) {
    throw new RuntimeException();
   }
   break;
  }
  if (reverse) {
   visited[newX][newY] = 0;
  }
  if (visited[newX][newY] == 0) {
   int target = board[newX][newY];
   board[x][y] = target;
   board[newX][newY] = 0;
   x = newX;
   y = newY;
   System.out.println(level + " slide " + direction.toString() + " to x " + x + " y " + y);
  } else {
   throw new RuntimeException();
  }
 }
 
 public enum Direction {
  Up, down, left, right
 }
 
 public static void main(String[] args) {
  TileBoard interview = new TileBoard();
//  System.out.println(interview.finalCheck());
  System.out.println(interview.toString());
//  interview.slide(Direction.Up);
//  System.out.println(interview.toString());
//  interview.slide(Direction.left);
//  System.out.println(interview.toString());
//  interview.slide(Direction.right);
//  System.out.println(interview.toString());
//  interview.slide(Direction.down);
//  System.out.println(interview.toString());
  interview.shuffle();
  System.out.println(interview.toString());
  interview.sovle();
  System.out.println(interview.toString());
  System.out.println(interview.finalCheck());
 }
 
 @Override
 public String toString() {
  StringBuilder sb = new StringBuilder();
  for (int i = 0; i < 3; i++) {
   if (i > 0) {
    sb.append("\n");
   }
   for (int j = 0; j < 3; j++) {
    sb.append(board[i][j]  + " ");
   }
  }
  return sb.toString();
 }
}