# Maze little problem

**URL:** <https://discourse.processing.org/t/maze-little-problem/30463>\
**Category:** Coding Questions\
**Tags:** homework\
**Created:** [June 3, 2021, 5:13am UTC](https://discourse.processing.org/t/maze-little-problem/30463 "2021-06-03T05:13:23Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![zang](https://avatars.discourse-cdn.com/v4/letter/z/bc8723/32.png) [@zang](https://discourse.processing.org/u/zang)\
**Post date:** [June 3, 2021, 5:13am UTC](https://discourse.processing.org/t/maze-little-problem/30463/1 "2021-06-03T05:13:23Z")

</div>

> ```auto
> int cols, rows;
> int w = 20;
> 
> ArrayList<Cell> grid = new ArrayList<Cell>();  
> ArrayList<Cell> stack = new ArrayList<Cell>();
> Cell current;
> 
> void setup() {
> size(820, 820);
> cols = floor(width/w);
> rows = floor(height/w);
> 
> for (int j = 0; j < rows; j++) {
> for (int i = 0; i < cols; i++) {
> Cell cell = new Cell(i, j);
> grid.add(cell);
> }
> }
> //initialized the wall
> for (int j = 0; j < rows/2+1; j++) {
> for (int i = 0; i < cols; i++) {
> grid.get(index(i, j*2 )).wall = true;
> }
> }
> 
> for (int j = 0; j < rows; j++) {
> for (int i = 0; i < cols/2+1; i++) {
> grid.get(index(i*2, j )).wall = true;
> }
> }
> 
> //frameRate(5);
> current = grid.get(index(1, 1));
> }
> 
> void draw() {
> background(51);
> for (int j = 0; j < rows; j++) {
> for (int i = 0; i < cols; i++) {
> grid.get(index(i, j)).show();
> }
> }
> current.visited = true;
> current.highlight();
> // STEP 1
> Cell next = current.checkNeighbors();
> if (next != null) {
> next.visited = true;
> 
> // STEP 2
> stack.add(current);
> 
> // STEP 3
> removeWalls(current, next);
> 
> // STEP 4
> current = next;
> } else if (stack.size() > 0) {
> current = stack.remove(stack.size()-1);
> }
> }
> 
> int index(int i, int j) {
> if (i < 0 || j < 0 || i > cols-1 || j > rows-1) {
> return 0;
> }
> return i + j * cols;
> }
> 
> void removeWalls(Cell a, Cell b) {
> int x = a.i - b.i;
> if (x == 2) {
> grid.get(index((a.i+b.i)/2, a.j)).wall = false;
> } else if (x == -2) {
> grid.get(index((a.i+b.i)/2, a.j)).wall = false;
> }
> int y = a.j - b.j;
> if (y == 2) {
> grid.get(index(a.i, (a.j+b.j)/2)).wall = false;
> } else if (y == -2) {
> grid.get(index(a.i, (a.j+b.j)/2)).wall = false;
> }
> 
> }
> 
> ```

```auto
class Cell {
  int i, j;
  boolean wall = false;
  boolean visited = false;
  
  ArrayList<Cell> neighborAstars = new ArrayList<Cell>();
  
  
  Cell(int i_, int j_) {
    i = i_;
    j = j_;
  }

  
 
  Cell checkNeighbors() {
    ArrayList<Cell> neighbors = new ArrayList<Cell>();

    Cell top = grid.get(index(i, j-2));
    Cell right = grid.get(index(i+2, j));
    Cell bottom = grid.get(index(i, j+2));
    Cell left = grid.get(index(i-2, j));

    if (top != null && !top.visited && !wall) {
      neighbors.add(top);
    }
    if (right != null && !right.visited && !wall) {
      neighbors.add(right);
    }
    if (bottom != null && !bottom.visited && !wall) {
      neighbors.add(bottom);
    } 
    if (left != null && !left.visited && !wall) {
      neighbors.add(left);
    }

    if (neighbors.size() > 0) {
      int r = floor(random(0, neighbors.size()));
      
      return neighbors.get(r);
    } else {
      return null;
    }
  }
  
  
  
    
  
   
   
   void show() {
    int x = i*w;
    int y = j*w;
    stroke(255);
    if(wall){
      noStroke();
      fill(0, 0, 255, 100);
      rect(x, y, w, w);
    }
      if(!wall){
      noStroke();
      fill(255);
      rect(x, y, w, w);
    }
    
    if (visited) {
      noStroke();
      fill(255);
      rect(x, y, w, w);
    }
  }
  
  
 
  void highlight() {
    int x = i*w;
    int y = j*w;
    noStroke();
    fill(0, 0, 255, 100);
    rect(x, y, w, w);

  }
  
  
  

}

```

why the grid(0,0) always turn wall to !wall.

---

<div class="post-metadata">

**Author:** ![jb4x](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/jb4x/32/789_2.png) [@jb4x](https://discourse.processing.org/u/jb4x)\
**Post date:** [June 3, 2021, 8:05pm UTC](https://discourse.processing.org/t/maze-little-problem/30463/2 "2021-06-03T20:05:31Z")

</div>

In your index function, you return 0 if i or j are out of bounds.

Since the first cell is at (1, 1) and when you check the neighboring cell at i - 2 and j - 2 you will return the cell at index 0 so the top left one.

Also be careful at your index function. It seems to me that it should be `return i + j * rows;` (I guess your indices go from top to bottom and then left to right).

---

<div class="post-metadata">

**Author:** ![zang](https://avatars.discourse-cdn.com/v4/letter/z/bc8723/32.png) [@zang](https://discourse.processing.org/u/zang)\
**Post date:** [June 4, 2021, 4:37am UTC](https://discourse.processing.org/t/maze-little-problem/30463/3 "2021-06-04T04:37:44Z")

</div>

really aperaciate for your carefullness, thanks a lot , it helps.

---

<div class="post-metadata">

**Author:** ![zang](https://avatars.discourse-cdn.com/v4/letter/z/bc8723/32.png) [@zang](https://discourse.processing.org/u/zang)\
**Post date:** [June 4, 2021, 5:18am UTC](https://discourse.processing.org/t/maze-little-problem/30463/4 "2021-06-04T05:18:49Z")

</div>

the grid(0,0) is already setted to wall. it means it will never be in arraylist neihbors,there is no way it turn wall to !wall.

and this problem i already fixed out by return 42,but i still confused.can you tell me more details.