Connect Four Spoilers

These spoilers are obsolete. You should be representing the board as a list of pieces. Detecting a win should have mostly been part of a warm-up in class.

Two problems with connect four: changing an entry in a matrix ([[Int]]) and seeing if there is a win.

Changing entries in the board

The biggest problem with the representation of the board as [[Int]] is that it is really hard to change the entries. If you use [((Int,Int),Player)] then it’s lots easier to make moves.

Outline of plan:

1. (changeCol: [Int] -> Int -> Int -> [Int]) Change value at index col in a single row to newVal; every other value in the list just output unchanged.

    changeCol [10,11,12] 2 99 == [10,11,99]

We have basically written this function as a Coding Bat problem.

2. (changeRowCol: [[Int]] -> Int -> Int -> Int -> [[Int]]) Run changeCol only on the index row entry, everything else stays the same.

    changeRowCol [[1,2,3,4],[5,6,7,8]] 1 3 99 == [[1,2,3,4],[5,6,7,99]]

There is actually spoiler code and fancy spoiler code that uses Chapter 6.

Detecting a win

Please email me questions. I know this is tricky. My own breakdown was:

1. Generate a list containing four ordered pairs in a row. Input: (x,y) coordinates of the first entry, and (dx,dy) to be added to (x,y) to get the other three pairs needed.

2. Given a board and one list of four ordered pairs, return True if all of the ordered pairs are legal coordinates for that board.

3. Given a board, return a list of all possible lists of four ordered pairs in straight lines. For example, if the board is just the flat 5x1 board [[0,0,0,0,0]], then this function should give a list of the two possible 4-in-a-rows: [[(0,0),(1,0),(2,0),(3,0)], [(1,0),(2,0),(3,0),(4,0)]].

4. Given a board and a single ordered pair, get the corresponding value from the board.

5. Given a board and four ordered pairs, return True if all of the corrsponding values are the same.

6. Do the preceding to a whole list of 4 pairs of coordinates.

7. Given a board, return True if it is won.

8. There are a few more steps but you are almost there!