Add diagonal win checks

Adds diagonal win checking, and tests to go along with them

connect4.c

@@ -74,12 +74,76 @@ int check_for_win_vertical(struct Board *board, size_t pos_i, size_t pos_j)
   return 0;
 }
 
+int check_for_win_lr_diagonal(struct Board *board, size_t pos_i, size_t pos_j)
+{
+  enum Tile current_player = board->next_player * -1;
+  char in_a_row = 1;
+  // Down-right
+  size_t npos_i = pos_i + 1;
+  size_t npos_j = pos_j + 1;
+  while (npos_i < board->width && npos_j < board->height &&
+      IDX(npos_i, npos_j, board) == current_player) {
+    in_a_row++;
+    npos_i++;
+    npos_j++;
+    if (in_a_row >= 4)
+      return 1;
+  }
+  // Up-left
+  npos_i = pos_i - 1;
+  npos_j = pos_j - 1;
+  while (npos_i < board->width && npos_j < board->height &&
+      IDX(npos_i, npos_j, board) == current_player) {
+    in_a_row++;
+    npos_i--;
+    npos_j--;
+    if (in_a_row >= 4)
+      return 1;
+  }
+
+  return 0;
+}
+
+int check_for_win_rl_diagonal(struct Board *board, size_t pos_i, size_t pos_j)
+{
+  enum Tile current_player = board->next_player * -1;
+  char in_a_row = 1;
+  // Down-left
+  size_t npos_i = pos_i - 1;
+  size_t npos_j = pos_j + 1;
+  while (npos_i < board->width && npos_j < board->height &&
+      IDX(npos_i, npos_j, board) == current_player) {
+    in_a_row++;
+    npos_i--;
+    npos_j++;
+    if (in_a_row >= 4)
+      return 1;
+  }
+  // Up-right
+  npos_i = pos_i + 1;
+  npos_j = pos_j - 1;
+  while (npos_i < board->width && npos_j < board->height &&
+      IDX(npos_i, npos_j, board) == current_player) {
+    in_a_row++;
+    npos_i++;
+    npos_j--;
+    if (in_a_row >= 4)
+      return 1;
+  }
+
+  return 0;
+}
+
 int check_for_win(struct Board *board, size_t pos_i, size_t pos_j)
 {
   if (check_for_win_horizontal(board, pos_i, pos_j))
       return 1;
   if (check_for_win_vertical(board, pos_i, pos_j))
       return 1;
+  if (check_for_win_lr_diagonal(board, pos_i, pos_j))
+      return 1;
+  if (check_for_win_rl_diagonal(board, pos_i, pos_j))
+      return 1;
   return 0;
 }
 

test_connect4.c

@@ -49,12 +49,109 @@ void test_middle_horizontal_win(void)
   free_board(board);
 }
 
+void test_ul_diagonal_win(void)
+{
+  struct Board *board = make_board(4,4);
+  /* X    9
+   * OX   87
+   * OOX  465
+   * OXOX 0123
+   */
+  int positions[] = {0, 1, 2, 3, 0, 2, 1, 1, 0};
+  drop_series(board, positions, 9);
+  int output = drop_tile(board, 0);
+  assert(output == 1 && "Upper Left Diagonal Win");
+  free_board(board);
+}
+
+void test_ur_diagonal_win(void)
+{
+  struct Board *board = make_board(4,4);
+  /*    X    9
+   *   XO   78
+   *  XOO  564
+   * XOXO 3210
+   */
+  int positions[] = {3, 2, 1, 0, 3, 1, 2, 2, 3};
+  drop_series(board, positions, 9);
+  int output = drop_tile(board, 3);
+  assert(output == 1 && "Upper Right Diagonal Win");
+  free_board(board);
+}
+
+
+void test_lr_diagonal_win(void)
+{
+  struct Board *board = make_board(4,4);
+  /* X    7
+   * OX   69
+   * OOX  485
+   * OXOX 0123
+   */
+  int positions[] = {0, 1, 2, 3, 0, 2, 0, 0, 1};
+  drop_series(board, positions, 9);
+  int output = drop_tile(board, 1);
+  assert(output == 1 && "Left-Right Middle Diagonal Win");
+  free_board(board);
+}
+
+void test_rl_diagonal_win(void)
+{
+  struct Board *board = make_board(4,4);
+  /*    X    7
+   *   XO   96
+   *  XOO  584
+   * XOXO 3210
+   */
+  int positions[] = {3, 2, 1, 0, 3, 1, 3, 3, 2};
+  drop_series(board, positions, 9);
+  int output = drop_tile(board, 2);
+  assert(output == 1 && "Right-Left Middle Diagonal Win");
+  free_board(board);
+}
+
+void test_br_diagonal_win(void)
+{
+  struct Board *board = make_board(4,4);
+  /* XO   38
+   * OXO  27A
+   * XXX  159
+   * OOOX 046B
+   */
+  int positions[] = {0, 0, 0, 0, 1, 1, 2, 1, 1, 2, 2};
+  drop_series(board, positions, 11);
+  int output = drop_tile(board, 3);
+  assert(output == 1 && "Bottom-Right Diagonal Win");
+  free_board(board);
+}
+
+void test_bl_diagonal_win(void)
+{
+  struct Board *board = make_board(4,4);
+  /*   OX   83
+   *  OXO  A72
+   *  XOO  951
+   * XOXO B640
+   */
+  int positions[] = {3, 3, 3, 3, 2, 2, 3, 2, 2, 1, 1};
+  drop_series(board, positions, 11);
+  int output = drop_tile(board, 0);
+  assert(output == 1 && "Bottom-left Diagonal Win");
+  free_board(board);
+}
+
 int main(int argc, char *argv[])
 {
   test_vertical_win();
   test_left_horizontal_win();
   test_right_horizontal_win();
   test_middle_horizontal_win();
+  test_ul_diagonal_win();
+  test_bl_diagonal_win();
+  test_rl_diagonal_win();
+  test_ur_diagonal_win();
+  test_br_diagonal_win();
+  test_lr_diagonal_win();
 
   return EXIT_SUCCESS;
 }