ConnectFour.java

public class ConnectFour {
 private int[][] board;
 //board : 0 : empty, 1 : player1, 2 : player2
 private int win;
 private int player;


 public ConnectFour(int row, int col, int win) {
 this.board = new int[row][col];
 this.win = win;
 this.player = 1;
 }

 /**
 *
 * @param col
 * @return The current element's position, [-1, -1] if player can not place the move
 */
 public int[] play(int col) {
 int[] pos = new int[2];
 int row = 0;
 // System.out.println(col);
 for (; row < board.length; row++) {
 //Find the first empty space
 if (board[row][col] == 0) break;
 }

 if (row < board.length) {
 board[row][col] = this.player;

 if (player == 1)
 player = 2;
 else
 player = 1;
 return new int[] {row, col};
 }
 return new int[] {-1, -1};

 }

 public void print() {

 for (int i = board.length - 1; i >= 0; i--) {
 for (int j = 0; j < board[0].length; j++) {
 if (board[i][j] == 1) {
 System.out.print('O');
 } else if (board[i][j] == 2) {
 System.out.print('X');
 } else {
 System.out.print('.');
 }
 }
 System.out.println();
 }
 }

 /**
 * i, j is the position in the board, return 0 if the game is not yet over, 1 if player1 win and 2 if player2 win
 * @param i
 * @param j
 * @return winner (1 or 2), not yet finished: 0, finish but no winner: -1
 */
 public int winner(int i, int j) {

 if (boardFull()) return -1;
 //Check row
 // left side consecutive + itself + right side consecutive
 if (rowConsecutive(i, j, -1) + 1 + rowConsecutive(i, j, 1) >= win) return board[i][j];
 // Bottom consecutive + itself +
 if (colConsecutive(i, j, -1) + 1 + colConsecutive(i, j, 1) >= win) return board[i][j];
 // Check two way diagonals
 if (diagonalConsecutive(i + 1, j + 1, 1, 1) + 1 + diagonalConsecutive(i - 1, j - 1, -1, -1) >= win) return board[i][j];
 if (diagonalConsecutive(i - 1, j + 1, -1, 1) + 1 + diagonalConsecutive(i + 1, j - 1, 1, -1) >= win) return board[i][j];
 System.out.print("cons: ");
 System.out.println(rowConsecutive(i, j, -1) + 1 + rowConsecutive(i, j, 1));
 return 0;
 }

 /**
 * Return how many consecutive consecutive elements in the row with given increment
 */
 private int rowConsecutive(int row, int col, int increment) {
 int player = this.board[row][col];
 if (player == 0) return 0;

 int res = 0;
 for (; col + increment < board[0].length && col + increment >= 0 && board[row][col + increment] == board[row][col]; col += increment, res += 1);

 return res;
 }

 /**
 * Return how many consecutive consecutive elements in the col with given increment
 */
 private int colConsecutive(int row, int col, int increment) {
 int player = this.board[row][col];
 if (player == 0) return 0;

 int res = 0;
 for (; row + increment < board.length && row + increment >= 0 && board[row + increment][col] == board[row][col]; row += increment, res += 1);
 return res;
 }

 /**
 *
 * @param row
 * @param col
 * @param ver: Indicate vertical direction: +1: up, -1: down
 * @param hor: Indicate horizontal direction, +1: top heads to right, -1: top heads to left
 * @return
 */
 private int diagonalConsecutive(int row, int col, int ver, int hor) {
 if (row >= board.length || col >= board.length || row < 0 || col < 0 || board[row - ver][col - hor] != board[row][col]) return 0;
 return 1 + diagonalConsecutive(row + ver, col + hor, ver, hor);
 }


 private boolean boardFull() {
 for (int col = 0; col < board[0].length; col++) {
 if (board[board.length - 1][col] == 0) return false;
 }
 return true;
 }

 public static void main(String[] args) {
 ConnectFour cf = new ConnectFour(9,9,5);
 System.out.println("Player1 moves \"O\" and Player2 two moves \"X\"");
 while (true) {
 int[] pos;
 while ((pos = cf.play((int)(Math.random() * 7)))[0] == -1);

 System.out.println();
 cf.print();
 int winner;
 if ((winner = cf.winner(pos[0], pos[1])) != 0) {
 if (winner == -1) { //No winner and game is finished
 System.out.println("No winner and the game is finished");
 break;
 } else {
 System.out.println("Winner is player" + winner);
 System.out.println("Player1 moves \"O\" and Player2 two moves \"X\"");
 break;
 }
 }
 }
 }
}