mattTea/ConnectFour-challenge5

JL coding challenge #5

Connect4

Solution to the JL coding challenge #05 using Kotlin & JUnit5

Game rules

This is a two player game where each player takes turns adding one of their coloured tokens to a grid.

The winner is the player who gets four of their tokens in a line which can be horizontal, vertical or diagonal.

Unlike noughts and crosses, gravity is at play so any token added to a column falls to the bottom of the column.

Only one token can occupy a position in the grid so tokens added to the same column stack up.

The grid is 7 columns wide by 6 rows deep and tokens are red and yellow.

Red always plays first.

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Problem description

Create a function called getGridStatus that takes an array of strings as input and return one of the following strings as output...

"Red plays next"
"Yellow plays next"
"Red wins"
"Yellow wins"
"Draw" // -> this means there are no empty spaces left on the grid 

The array of strings used as the input is structured so that each string represents a row in the Connect4 grid...

• The element at position zero represents the top of the grid and the element with the highest position represents the bottom of the grid
• Each character in the string represents a column position in the grid, they can be any of the following...

"." // -> Empty position
"r" // -> Position contains a red token
"y" // -> Position contains a yellow token
"R" // -> Position contains a red token that was the last token added to the grid
"Y" // -> Position contains a yellow token that was the last token added to the grid

(If a grid contains tokens then one of the tokens should be either “R” or “Y” but the grid can’t contain both “R” and “Y”.)

Grid status examples

getGridStatus( [".......",
                ".......",
                ".......",
                ".......",
                ".......",
                "......."]) // -> "Red plays next"


getGridStatus( [".......",
                ".......",
                ".R.....",
                ".r.....",
                ".ry....",
                ".ryyy.."]) // -> "Red wins"


getGridStatus( [".......",
                ".......",
                ".......",
                ".yy....",
                ".rrRr..",
                ".ryyy.."]) // -> "Red wins"


getGridStatus( [".......",
                ".......",
                "....r..",
                "...ry..",
                "..Ryr..",
                ".ryyyr."] ) // -> "Red wins"


getGridStatus( [".......",
                ".......",
                "...y...",
                "...ry..",
                "...ryy.",
                "...rrrY"]) // -> "Yellow wins"


getGridStatus( [".......",
                ".......",
                ".......",
                "...ry..",
                "...ryy.",
                "..yrrrY"]) // -> "Red plays next"


getGridStatus( [".......",
                ".......",
                ".......",
                "...ry..",
                "..Rryy.",
                "..yrrry"]) // -> "Yellow plays next"

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Problem breakdown

1. getGridStatus returns a string

2. getGridStatus returns "Red plays next" for empty grid

3. getGridStatus returns "Draw" for full grid

4. getGridStatus returns "Yellow plays next" for grid with "R" present

5. getGridStatus returns "Red plays next" for grid with "Y" present

6. getGridStatus returns "Red wins" for 4 horizontal reds

7. getGridStatus returns "Yellow wins" for 4 horizontal yellows

8. getGridStatus returns "Red wins" for 4 vertical reds

   • Transpose grid
   • Then check whether they are in same horizontal row as above

9. getGridStatus returns "Yellow wins" for 4 vertical yellows

10. TODO... getGridStatus returns "Red wins" for 4 diagonal reds

11. TODO... getGridStatus returns "Yellow wins" for 4 diagonal yellows