2024 day 6, brute force.

src/holt59/aoc/2024/day6.py

@@ -1,10 +1,106 @@
 import sys
+from typing import TypeAlias
+
+
+def move(
+    lines: list[str], pos: tuple[int, int], dir: tuple[int, int]
+) -> tuple[tuple[int, int] | None, list[tuple[int, int]]]:
+    n_rows, n_cols = len(lines), len(lines[0])
+    row, col = pos
+    marked: list[tuple[int, int]] = []
+
+    while True:
+        marked.append((row, col))
+
+        if not (0 <= row + dir[0] < n_rows and 0 <= col + dir[1] < n_cols):
+            pos = None
+            break
+
+        if lines[row + dir[0]][col + dir[1]] != ".":
+            pos = (row, col)
+            break
+
+        row += dir[0]
+        col += dir[1]
+
+    return pos, marked
+
+
+def print_grid(
+    lines: list[str], marked: set[tuple[int, int]], current_pos: tuple[int, int] | None
+):
+    chars = list(map(list, lines))
+
+    for i, j in marked:
+        chars[i][j] = "X"
+
+    if current_pos:
+        chars[current_pos[0]][current_pos[1]] = "T"
+
+    for line in chars:
+        print("".join(line))
+    print()
+
+
+ROTATE = {(-1, 0): (0, 1), (0, 1): (1, 0), (1, 0): (0, -1), (0, -1): (-1, 0)}
+
 
 lines = sys.stdin.read().splitlines()
+n_rows, n_cols = len(lines), len(lines[0])
+start_pos = next(
+    (i, j) for i in range(n_rows) for j in range(n_cols) if lines[i][j] == "^"
+)
+lines[start_pos[0]] = lines[start_pos[0]].replace("^", ".")
 
-answer_1 = ...
+# part 1
+marked: set[tuple[int, int]] = set()
 
-answer_2 = ...
+current_pos: tuple[int, int] | None = start_pos
+current_dir = (-1, 0)
+
+while current_pos is not None:
+    # print_grid(lines, marked, current_pos)
+    new_pos, new_marked = move(lines, current_pos, current_dir)
+
+    marked = marked.union(new_marked)
+
+    current_pos = new_pos
+    current_dir = ROTATE[current_dir]
+
+# print_grid(lines, marked, current_pos)
+
+answer_1 = len(marked)
+
+answer_2 = 0
+for row in range(n_rows):
+    for col in range(n_cols):
+        if (row, col) == start_pos or lines[row][col] != ".":
+            continue
+
+        chars = list(map(list, lines))
+
+        chars[row][col] = "#"
+
+        current_pos = start_pos
+        current_dir = (-1, 0)
+
+        found: set[tuple[tuple[int, int], tuple[int, int]]] = set()
+
+        while current_pos is not None:
+            if current_pos != start_pos:
+                found.add((current_pos, current_dir))
+
+            new_pos, new_marked = move(
+                ["".join(line) for line in chars], current_pos, current_dir
+            )
+
+            current_pos = new_pos
+            current_dir = ROTATE[current_dir]
+
+            if (current_pos, current_dir) in found:
+                print(row, col)
+                answer_2 += 1
+                break
 
 print(f"answer 1 is {answer_1}")
 print(f"answer 2 is {answer_2}")