feat: share edges between neighboring tiles

3 files changed, 65 insertions, 57 deletions

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..6e455d0
--- /dev/null
+++ b/README.md
@@ -0,0 +1,11 @@
+# Board example
+Here's example 3x2 board:
+```
+ F C
+RRRRC*
+ F R
+ *FRF*
+   R
+```
+
+Stars `*` symbolize available centers tile placement.
diff --git a/src/board.h b/src/board.h
index 442b03d..f5d2da3 100644
--- a/src/board.h
+++ b/src/board.h
@@ -1,12 +1,15 @@
-#define TILE_SIZE 5
-#define BOARD_WIDTH 6
-#define BOARD_BYTES TILE_SIZE * (BOARD_WIDTH * BOARD_WIDTH)
+#define BOARD_WIDTH 2
+#define BOARD_ROW_BYTES ((BOARD_WIDTH * 2) + 1)
+#define BOARD_BYTES BOARD_ROW_BYTES * BOARD_ROW_BYTES
 
-int direction_increments[] = {
-  - TILE_SIZE * BOARD_WIDTH + 2,
-    TILE_SIZE               + 2,
-    TILE_SIZE * BOARD_WIDTH - 2,
-  - TILE_SIZE               - 2
+char EMPTY = ' ';
+char FORBIDDEN = ' ';
+
+int neighbor_increments[] = {
+  - BOARD_ROW_BYTES,
+    1,
+    BOARD_ROW_BYTES,
+  - 1
 };
 
 // Board
@@ -15,7 +18,8 @@ void initialize_board(char* board);
 void print_board(char* board);
 
 // Moves
-int check_allowed_tile(char* tile, int position, char* board);
+int is_allowed_placement(char* tile, int position, char* board);
 
-void place_tile(char* tile, int position, char* board);
+int is_center_position(int position);
 
+int place_tile(char* tile, int position, char* board);
diff --git a/src/main.c b/src/main.c
index 71ae7f3..a872cab 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,69 +1,62 @@
+#include <stdio.h>
 #include "board.h"
 
-
-int check_allowed_tile(char* tile, int position, char* board) {
-  for (int i = 0; i < 4; i++) {
-    int index = (position * TILE_SIZE + i) + direction_increments[i];
-    printf("Checking board index %i\n", index);
-    // TODO: board should have sentinel row/column
-    if (index >= 0 && index < BOARD_BYTES) {
-      char neighboring_edge = board[index];
-      if (neighboring_edge > 0 && neighboring_edge != tile[i] && neighboring_edge != '_') {
-        printf("Failed on edge %i (%c). Neighboring edge is %c\n", i, tile[i], neighboring_edge);
-        return 0;
-      }
+void print_board(char* board) {
+  for (int row = 0; row < BOARD_ROW_BYTES; row++) {
+    for (int i = 0; i < BOARD_ROW_BYTES; i++) {
+      int position = BOARD_ROW_BYTES * row + i;
+      if (board[position] == EMPTY && is_center_position(position)) printf("*");
+      else printf("%c", board[position]);
     }
+    printf("\n");
   }
-  return 1;
 }
 
-void place_tile(char* tile, int position, char* board) {
-  if (!check_allowed_tile(tile, position, board)) {
-    printf("Could not place the tile!");
-    return;
-  }
-  for (int i = 0; i < TILE_SIZE; i++) {
-    board[position * TILE_SIZE + i] = tile[i];
+void initialize_board(char* board) {
+  for (int i = 0; i < BOARD_BYTES; i++) {
+    board[i] = EMPTY;
   }
 }
 
-void print_board(char* board) {
-  for (int row = 0; row < BOARD_WIDTH; row++) {
-    for (int tile = 0; tile < BOARD_WIDTH; tile++) {
-      printf("_%c_", board[TILE_SIZE * (row * BOARD_WIDTH + tile)]);
-    }
-    printf("\n");
-    for (int tile = 0; tile < BOARD_WIDTH; tile++) {
-      printf(
-          "%c%c%c",
-          board[TILE_SIZE * (row * BOARD_WIDTH + tile) + 3],
-          board[TILE_SIZE * (row * BOARD_WIDTH + tile) + 4],
-          board[TILE_SIZE * (row * BOARD_WIDTH + tile) + 1]
-      );
-    }
-    printf("\n");
-    for (int tile = 0; tile < BOARD_WIDTH; tile++) {
-      printf("_%c_", board[TILE_SIZE * (row * BOARD_WIDTH + tile) + 2]);
-    }
-    printf("\n");
+int is_center_position(int position) {
+  return ((position / BOARD_ROW_BYTES) % 2 == 1) && ((position % BOARD_ROW_BYTES) % 2 == 1);
+}
+
+int is_allowed_placement(char* tile, int position, char* board) {
+  for (int i = 0; i < 4; i++) {
+    char neighbor = board[position + neighbor_increments[i]];
+    if (neighbor != EMPTY && neighbor != tile[i + 1]) return 0;
   }
+  return 1;
 }
 
-void initialize_board(char* board) {
-  for (int i = 0; i < BOARD_BYTES; i++) {
-    board[i] = '_';
+int place_tile(char* tile, int position, char* board) {
+  if (!is_center_position(position)) {
+    printf("Not a valid tile position: %i\n", position);
+    return 0;
   }
+
+  if (!is_allowed_placement(tile, position, board)) {
+    printf("Can not place tile %s\n", tile);
+    return 0;
+  }
+
+  board[position] = tile[0];
+  for (int i = 0; i < 4; i++) {
+    board[position + neighbor_increments[i]] = tile[i + 1];
+  }
+
+  return 1;
 }
 
 int main() {
-  // Board
   char board[BOARD_BYTES];
   initialize_board(board);
 
-  place_tile("ABCDE", 7, board);
-  place_tile("FGHBJ", 8, board);
-  place_tile("FGHGJ", 9, board);
-  place_tile("FGAGJ", 1, board);
+  place_tile("RFRFR", 6, board);
+  place_tile("RCCRR", 8, board);
+  place_tile("RRFRF", 18, board);
+  place_tile("CFFFC", 16, board);
 
   print_board(board);