day 13

aoc2023/day13.py

@@ -0,0 +1,101 @@
+import pathlib
+from collections.abc import Iterable
+
+base_dir = pathlib.Path(__file__).parent
+filename = base_dir / "day13_input.txt"
+
+with open(base_dir / filename) as f:
+    lines: list[str] = f.read().splitlines()
+
+Grid = list[list[str]]
+grids: list[Grid] = []
+
+grid: Grid = []
+
+for line in lines:
+    if line == "":
+        if grid:
+            grids.append(grid)
+            grid = []
+    else:
+        grid.append(list(line))
+
+if grid:
+    grids.append(grid)
+
+
+def print_grid(grid: Grid) -> None:
+    for row in grid:
+        print("".join(row))
+
+
+def get_sequence_symmetries(
+    sequence: list[str],
+    indices: Iterable[int],
+) -> set[int]:
+    width = len(sequence)
+    symmetry: set[int] = set()
+
+    for x in indices:
+        comparison_width = min(x, width - x)
+        start_a = max(0, x - comparison_width)
+        end_a = x
+        start_b = x
+        end_b = x + comparison_width
+
+        this_row = sequence[start_a:end_a]
+        other_row = list(reversed(sequence[start_b:end_b]))
+
+        if this_row == other_row:
+            symmetry.add(x)
+
+    return symmetry
+
+
+def get_grid_score(grid: Grid, missing_allowed: int) -> int:
+    width = len(grid[0])
+    height = len(grid)
+
+    row_symmetries = {k: 0 for k in set(range(1, width))}
+    col_symmetries = {k: 0 for k in set(range(1, height))}
+
+    for row in grid:
+        symmetries = get_sequence_symmetries(row, row_symmetries)
+
+        for k in symmetries:
+            row_symmetries[k] += 1
+
+    for col_idx in range(width):
+        col = [row[col_idx] for row in grid]
+        symmetries = get_sequence_symmetries(col, col_symmetries)
+        for k in symmetries:
+            col_symmetries[k] += 1
+
+    if missing_allowed:
+        for k, v in row_symmetries.items():
+            if v == height - 1:
+                return k
+        for k, v in col_symmetries.items():
+            if v == width - 1:
+                return 100 * k
+
+    for k, v in row_symmetries.items():
+        if v == height:
+            return k
+    for k, v in col_symmetries.items():
+        if v == width:
+            return 100 * k
+
+    return -9999999
+
+
+def part_1():
+    return sum(get_grid_score(grid, missing_allowed=0) for grid in grids)
+
+
+def part_2():
+    return sum(get_grid_score(grid, missing_allowed=1) for grid in grids)
+
+
+print(f"answer_p1: {part_1()}")
+print(f"answer_p2: {part_2()}")

aoc2023/day13_test.txt

@@ -0,0 +1,15 @@
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#