Implement day 8 solver

puzzles/8.py

@@ -0,0 +1,110 @@
+from itertools import combinations
+from typing import NamedTuple
+
+test_input = """
+............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............
+""".strip()
+
+test_solution_p1 = 14
+test_solution_p2 = 34
+
+
+def solve_p1(puzzle_input: str) -> int:
+    grid = _parse_signal_grid(puzzle_input)
+    antinodes = _calculate_antinodes(grid)
+    # _print_grid(grid, antinodes)
+    return len(antinodes)
+
+
+def solve_p2(puzzle_input: str) -> int:
+    grid = _parse_signal_grid(puzzle_input)
+    antinodes = _calculate_antinodes(grid, harmonic=True)
+    # _print_grid(grid, antinodes)
+    return len(antinodes)
+
+
+class Point(NamedTuple):
+    x: int
+    y: int
+
+
+class SignalGrid(NamedTuple):
+    width: int
+    height: int
+    antenna_arrays: dict[str, set[Point]]
+
+
+def _parse_signal_grid(puzzle_input: str) -> SignalGrid:
+    lines = puzzle_input.strip().split("\n")
+    antenna_arrays: dict[str, set[Point]] = {}
+
+    for x, line in enumerate(lines):
+        for y, char in enumerate(line):
+            if char.isalnum():
+                if char not in antenna_arrays:
+                    antenna_arrays[char] = set()
+                antenna_arrays[char].add(Point(x, y))
+
+    return SignalGrid(len(lines[0]), len(lines), antenna_arrays)
+
+
+def _calculate_antinodes(grid: SignalGrid, harmonic=False) -> set[Point]:
+    antinodes: set[Point] = set()
+
+    for antenna_array in grid.antenna_arrays.values():
+        for a, b in combinations(antenna_array, 2):
+            dx = b.x - a.x
+            dy = b.y - a.y
+
+            # Left antinodes
+            if harmonic:
+                antinode = a
+                while True:
+                    antinodes.add(antinode)
+                    antinode = Point(antinode.x - dx, antinode.y - dy)
+                    if not _is_in_grid(grid, antinode):
+                        break
+            else:
+                antinode = Point(a.x - dx, a.y - dy)
+                if _is_in_grid(grid, antinode):
+                    antinodes.add(antinode)
+
+            # Right antinodes
+            if harmonic:
+                antinode = b
+                while True:
+                    antinodes.add(antinode)
+                    antinode = Point(antinode.x + dx, antinode.y + dy)
+                    if not _is_in_grid(grid, antinode):
+                        break
+            else:
+                antinode = Point(b.x + dx, b.y + dy)
+                if _is_in_grid(grid, antinode):
+                    antinodes.add(antinode)
+
+    return antinodes
+
+
+def _is_in_grid(grid: SignalGrid, point: Point) -> bool:
+    return 0 <= point.x < grid.height and 0 <= point.y < grid.width
+
+
+def _print_grid(grid: SignalGrid, antinodes: set[Point]):
+    output = [["."] * grid.width for _ in range(grid.height)]
+    for antinode in antinodes:
+        output[antinode.x][antinode.y] = "#"
+    for frequency, antenna_array in grid.antenna_arrays.items():
+        for antenna in antenna_array:
+            output[antenna.x][antenna.y] = frequency
+    print("\n".join("".join(row) for row in output))