迷宫生成prim算法并非遍历所有细胞

我正在尝试实现Prim迷宫生成算法：

• 从一个满墙的网格开始 .

• 选择一个单元格，将其标记为迷宫的一部分 . 将单元格的墙添加到墙列表中 .

• 虽然列表中有墙：

• 从列表中选择一个随机墙 . 如果细胞在另一侧
  尚未进入迷宫：

• 将墙壁作为通道，并将对面的单元格标记为迷宫的一部分 .

• 将单元格的相邻墙添加到墙列表中 .

• 如果对面的单元格已经在迷宫中，请从列表中删除墙壁 .

删除一些实现细节，我的实现如下所示：

Cell[][] maze

是带有细胞的矩阵 . 每个单元格都有左/右/上/按钮墙 . 边界墙标记为 boolean frontier ，并不是实施的一部分，因为我想保持我的迷宫框架 .

public Cell[][] prim(){
    List<Wall> walls = new ArrayList<Wall>();

    //Pick a cell, mark it as part of the maze
    int initialCellI = rnd(sizeX)-1;
    int initialCellJ = rnd(sizeY)-1;
    Cell randomCell = maze[initialCellI][initialCellJ];
    randomCell.setPartOftheMaze(true);

    //Add the walls of the cell to the wall list.
    if ((randomCell.getLeft() != null) && (!randomCell.getLeft().isFrontier()))
        walls.add(randomCell.getLeft());
    if ((randomCell.getRight() != null) && (!randomCell.getRight().isFrontier()))
        walls.add(randomCell.getRight());
    if ((randomCell.getButtom() != null) && (!randomCell.getButtom().isFrontier()))
        walls.add(randomCell.getButtom());
    if ((randomCell.getUp() != null) && (!randomCell.getUp().isFrontier()))
        walls.add(randomCell.getUp());

    //While there are walls in the list:
    while (!walls.isEmpty()){

        //Pick a random wall from the list.
       Wall randomWall = randomElement(walls);
       //pick the cell opposite to this wall. 
       Cell opositeSideCell = getNeightbourCell(randomWall, maze);
       if (opositeSideCell.isPartOftheMaze()){
           //If the cell on the opposite side already was in the maze, remove the wall from the list.
           walls.remove(randomWall);
       }
       else{
          // Make the wall a passage and mark the cell on the opposite side as part of the maze.
           this.removeWall(randomWall, maze);
           opositeSideCell.setPartOftheMaze(true);

            //Add the walls of the cell to the wall list.
            if ((opositeSideCell.getLeft() != null) && (!opositeSideCell.getLeft().isFrontier()))
                walls.add(opositeSideCell.getLeft());
            if ((opositeSideCell.getRight() != null) && (!opositeSideCell.getRight().isFrontier()))
                walls.add(opositeSideCell.getRight());
            if ((opositeSideCell.getButtom() != null) && (!opositeSideCell.getButtom().isFrontier()))
                walls.add(opositeSideCell.getButtom());
            if ((opositeSideCell.getUp() != null) && (!opositeSideCell.getUp().isFrontier()))
                walls.add(opositeSideCell.getUp());   
       }
    }
    return maze;
}

我的问题是我的迷宫没有完成，并没有遍历所有的细胞 . 有时只有几个细胞遍历，几乎所有细胞都已完成 . 我相信我错过了什么bur无法弄清楚是什么 .

请帮忙 .

部分遍历的迷宫见下图 .