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import sys
def traverse(room: list[list[str]], guard_current_row: int, guard_current_col: int, direct: tuple[int, int], check_for_loop: bool) -> bool:
row_count = len(room)
col_count = len(room[0])
previous_directions: list[list[list[tuple[int, int]]]] = []
for _ in range(row_count):
previous_directions.append([])
for _ in range(col_count):
previous_directions[-1].append([])
while True:
if not check_for_loop:
room[guard_current_row][guard_current_col] = "X"
else:
if direct in previous_directions[guard_current_row][guard_current_col]:
return True
previous_directions[guard_current_row][guard_current_col].append(direct)
new_row_idx = guard_current_row + direct[0]
new_col_idx = guard_current_col + direct[1]
if new_row_idx < 0 or new_row_idx >= row_count or new_col_idx < 0 or new_col_idx >= col_count:
break
if room[new_row_idx][new_col_idx] == "#":
dir_idx = directions.index(direct)
if dir_idx == len(directions) - 1:
dir_idx = 0
else:
dir_idx += 1
direct = directions[dir_idx]
else:
guard_current_row = new_row_idx
guard_current_col = new_col_idx
return False
lines = []
with open("input") as f:
for line in f.readlines():
lines.append(list(line.strip()))
found_guard = False
guard_row_idx = None
guard_col_idx = None
direction = None
directions = [(-1, 0), (0, 1), (1, 0), (0, -1)]
for line_idx, line in enumerate(lines):
for icon_idx, guard_icon in enumerate(("^", ">", "v", "<")):
if guard_icon in line:
guard_row_idx = line_idx
guard_col_idx = line.index(guard_icon)
direction = directions[icon_idx]
found_guard = True
break
if found_guard:
break
if not found_guard:
sys.exit("Could not found guard.")
traverse(lines, guard_row_idx, guard_col_idx, direction, False)
count = 0
for row_idx, line in enumerate(lines):
for col_idx, char in enumerate(line):
if char == "X":
lines[row_idx][col_idx] = "#"
if traverse(lines, guard_row_idx, guard_col_idx, direction, True):
count += 1
lines[row_idx][col_idx] = "X"
print(count)
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