CS173: Intro to Computer Science - Four in a Row (3 Points)

Developed by Professor Tralie and Professor Mongan.

Exercise Goals

The goals of this exercise are:

1. To iterate over a 2-dimensional array

Modify the FourInARow.java file to return whether a given array contains a winning configuration. Specifically, if any column has four consecutive items with the same value, they are a winner.

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FourInARow.java

public class FourInARow { public static int checkWinning(int[][] board) { // winner is 0 if there is no winner, 1 if team 1 wins, // ... and 2 if team 2 wins. int winner = 0; // the counts are the number of consecutive entries for team 1, // ... or team 2 in a particular column int count1 = 0; int count2 = 0; // this outer loop counts over all the rows, and we would normally // ... iterate across each row with the inner loop // ... but we want to loop down every column, so I'm switching the // ... i and j indices so that we loop down each column instead! // the number of columns is board[0].length - the size of the first row // ... (we'll assume they're all the same, so we'll just pick the first one!) for(int j = 0; j < board[0].length; j++) { // TODO: initialize count1 and count2 to 0 so that we have a // ... fresh count within each column // now, loop down each of the columns to look for a winner // the number of rows is board.length for(int i = 0; i < board.length; i++) { // TODO: if board[i][j] is 1, tally one for team1's count, // ... and similarly, if board[i][j] is 2, tally 1 for team2. // ... BUT, also reset the other team's count to 0 (since they // ... can't be winning if they don't have 4 in a row!). // ... what should you do in the "else" clause here, // ... if board[i][j] is 0? // TODO: if count1 or count2 is 4, set winner to 1 (if count1 is 4), // ... or 2 (if count2 is 4) } } return winner; } }

Driver.java

public class Driver { public static void main(String[] args) { int[][] board1 = new int[][] { { 0, 0, 1, 0 }, { 0, 2, 1, 1 }, { 0, 2, 1, 1 }, { 0, 2, 1, 1 } }; int[][] board2 = new int[][] { { 0, 0, 2, 0 }, { 0, 2, 1, 1 }, { 0, 2, 1, 1 }, { 0, 2, 1, 1 } }; int[][] board3 = new int[][] { { 0, 2, 2, 0 }, { 0, 2, 1, 1 }, { 0, 2, 1, 1 }, { 0, 2, 1, 1 } }; int winner1 = FourInARow.checkWinning(board1); int winner2 = FourInARow.checkWinning(board2); int winner3 = FourInARow.checkWinning(board3); System.out.print(winner1 + "-" + winner2 + "-" + winner3); } }

Driver.main(null);

Program Output

In this exercise, you will fill in a function to determine the winner of a game of Four-in-a-Row. A game board (a 2D array of ints) initially contains all 0s. Each player (team 1 and 2) places a value into a column of the game board, and it falls to the bottom of the board. The game ends with a winner if the board contains four consecutive items down a column (only the vertical column - you don’t need to worry about the rows or diagonals). For example, this board represents a game won by team 2:

int[][] board = new int[][] {
    { 0, 2, 2, 0 },
    { 0, 2, 1, 1 },
    { 0, 2, 1, 1 },
    { 0, 2, 1, 1 }
};