solve day 4 part 1

day_04/program.py

@@ -7,10 +7,58 @@ def get_lines(filename: str) -> list:
         return [line.strip() for line in file.readlines()]
 
 
-def main():
-    lines = get_lines("sample-input.txt")
-    # lines = get_lines("input.txt")
+def get_grid(lines: list) -> list:
+    grid = []
+    for line in lines:
+        row = []
+        for char in line:
+            row.append(char)
+        grid.append(row)
+    return grid
 
 
+def check_xmas_from_pos(grid: list, row: int, col: int,
+                        direction: tuple, xmas_letters: list) -> bool:
+    if grid[row][col] != xmas_letters[0]:
+        # wrong letter, end of recursion
+        return False
+
+    if len(xmas_letters) == 1:
+        # found the last letter, end of recursion
+        return True
+
+    # out of bounds, end of recursion
+    new_row = row + direction[0]
+    new_col = col + direction[1]
+    if new_row < 0 or new_row >= len(grid):
+        return False
+    if new_col < 0 or new_col >= len(grid[0]):
+        return False
+
+    # go deeper into recursion with one less letter on the search string
+    return check_xmas_from_pos(grid, new_row, new_col, direction, xmas_letters[1:])
+
+
+def get_xmas_appearances(grid: list) -> int:
+    xmas_appearances = 0
+    directions = [(0, 1), (1, 1), (1, 0), (1, -1), (0, -1), (-1, -1), (-1, 0), (-1, 1)]
+    xmas_letters = ['X', 'M', 'A', 'S']
+    for row in range(len(grid)):
+        for col in range(len(grid[0])):
+            for direction in directions:
+                if check_xmas_from_pos(grid, row, col, direction, xmas_letters):
+                    print(f"Found XMAS at position ({row}, {col}) in direction {direction}")
+                    xmas_appearances += 1
+    return xmas_appearances
+
+
+def main():
+    # lines = get_lines("sample-input.txt")
+    lines = get_lines("input.txt")
+
+    grid = get_grid(lines)
+    xmas_appearances = get_xmas_appearances(grid)
+    print(f"Part 1: The word XMAS appears {xmas_appearances} times.")
+
 if __name__ == '__main__':
     main()