Assignment 9: Minesweeper

Goals: Design a game with mutable world state, ArrayLists, mutable linked data structures, and loops.

This assignment is due in two parts.

Part 1: Due March 28th, at 9pm

Part 2: Due April 4th, at 9pm

Problem 1: Minesweeper

9.1 Introduction

For this project, you will be implementing the famous time-wasting game known since the 1960s, and popularized by Microsoft Windows 3.1, Minesweeper. The game consists of a two-dimensional grid of cells, with each cell possibly containing a hidden mine. The player can reveal what’s in a cell by clicking on it; there are three possibilities. First and most importantly, if it contains a mine, the player loses. Second, if the cell is empty but adjacent to some mines, the revealed cell shows a number indicating how many of its neighboring cells contain a mine.

Finally, if the revealed cell is both empty and has no neighbors with a mine, then instead of showing a zero, all of its neighbors are revealed, as well. This should cause a cascading “flood-fill” effect where an entire region of connected cells without mines is uncovered (play the game at the above link to see this in action). The flood-fill should stop when it reaches a cell with a non-zero neighboring mine count.

If the player clicks the cell in the top-right corner, the cell shows the number of adjacent mines (in this case, 1):

On the other hand, the cell in the lower-right corner has no adjacent mines. If the player clicked that cell instead, this would trigger the flood-fill behaivor, continuously spreading out and revealing all neighboring cels, stopping at cells that have adjacent mines:

In that screenshot, it’s obvious that there must be two mines in the middle of the bottom row. A player can indicate the location of a suspected mine by right-clicking a cell to place a flag on it (here shown as an orange triangle on the right-most cell):

The player’s goal is to identify where all of the mines are by uncovering all of the cells except the ones that contain mines. (The mines do not need to be flagged; they’re only for the player’s convenience.)

9.2 Prerequisites

9.3 Part 1

For the first part of the assignment, design the representation of the game and the initial drawing functionality. At a high level, you should:

• Design classes for the game, cells, and any other parts of the game you might need to represent. The game linked above uses a 30x16 grid with 99 mines, but both the grid size and number of mines should be easy to change in your solution. Thus, you should have a constructor in your World class which takes in the number of rows, the number of columns and the number of mines. You may put restrictions on how big or how small these numbers can be, but you should be able to handle a 30x16 grid.

• Link the cells together when the game is initialized so that every cell has a list of its neighbors. (This will create a cyclic structure, where neighboring cells have references to each other.) Once a node has this list, it should not need to know anything about its position in the grid to implement the rest of its functionality. In particular, a cell should not need or have fields representing its row/column position in the grid.

• Generate the random placement of mines using a Random object. You should supply a specific, seeded Random object in your game’s constructor for use in testing, and you should leave it unspecified for actual play. Hint: Using a counted-for loop to loop exactly \(N\) times generate \(N\) random coordinates is not sufficient, because you might end up generating the same coordinate twice: you need to produce \(N\) distinct mines.

• Implement a method to count the number of mines neighboring a particular cell. This will likely be simplified by having some simple way to iterate over all the neighbors of a cell.

• Implement the methods to draw the game board. In order to test your drawing, you may have to create an “intermediate” game board (similar to the screen shot above) to ensure that your drawing works for all types of cells. You can do so currently by creating more convenience constructors as necessary. You should not create any additional methods that only help you to test, but do not help in the actual game play.

9.4 Part 2

For this part of the assignment, finish implementing the game. That means:

• Implement left-mouse-click handling to reveal cells, including the flood-fill effect for cells with no adjacent mines.

• Implement right-mouse-click handling to flag/unflag cells.

• Check for win/loss conditions and end the game with an appropriate win or lose message. For this assignment, you don’t have to start a new game once a previous game ends (although you are welcome to do that if you like).

Note: To implement the flood-fill behavior, you will very much want the ability to iterate over the neighbors of a cell, without having to mess about with their coordinates. If you did not get this working in Part 1, fix it now.

Note: To have enough information to handle left and right clicks, you will need to override the two-argument form of onMouseClicked, that takes a Posn for the mouse position, and a String describing which button ("LeftButton", "MiddleButton", "RightButton" or "UnknownButton") was clicked.

Extra credit

If you would like to elaborate on this game for extra credit, there are several possibilities, of varying degrees of difficulty:

• Enhance the graphics to display how many mines remain to be uncovered, or how many cells, or how many clicks, or “keep score” in some fashion.

• Restart the game with a new layout of mines, after the game is over.

• Allow the player to select the game difficulty (board size or number of mines) before playing.