2022 day 14

Author: ianroberts

2022/14/sandfall.py

@@ -0,0 +1,99 @@
+from itertools import pairwise
+
+from aoc_common.grid import Cell, Direction
+
+
+def load_data():
+    blocked: set[Cell] = set()
+    with open("input", "r") as f:
+        for path in f:
+            path = path.strip()
+            corners = []
+            for corner in path.split(" -> "):
+                c, r = corner.split(",")
+                corners.append(Cell(int(r), int(c)))
+            for a, b in pairwise(corners):
+                a_to_b = b - a
+                if a_to_b.col == 0:
+                    vec = a_to_b // (abs(a_to_b.row))
+                else:
+                    vec = a_to_b // abs(a_to_b.col)
+
+                blocked.add(a)
+                while a != b:
+                    a += vec
+                    blocked.add(a)
+
+    return blocked
+
+
+def part1():
+    blocked = load_data()
+    walls = blocked.copy()
+    bottom_row = max(r for (r, c) in blocked)
+
+    units_of_sand = 0
+    done = False
+    while not done:
+        pos = Cell(0, 500)
+        while True:
+            if pos.row >= bottom_row:
+                # sand is trickling into the void
+                done = True
+                break
+            if ((candidate := pos + Direction.SOUTH) not in blocked) or ((candidate := pos + Direction.SW) not in blocked) or ((candidate := pos + Direction.SE) not in blocked):
+                # this unit of sand can move somewhere - move it
+                pos = candidate
+            else:
+                # this unit of sand cannot move, it has come to rest
+                blocked.add(pos)
+                units_of_sand += 1
+                break
+
+    min_col = min(c for r, c in blocked)
+    max_col = max(c for r, c in blocked)
+
+    for r in range(bottom_row + 2):
+        print("".join("#" if Cell(r, c) in walls else "o" if Cell(r, c) in blocked else "." for c in range(min_col-2, max_col+3)))
+
+
+    print(f"Units of sand that can come to rest: {units_of_sand}")
+
+
+def part2():
+    blocked = load_data()
+    walls = blocked.copy()
+    floor = max(r for (r, c) in blocked) + 2
+
+    def is_free(c: Cell):
+        return c.row != floor and c not in blocked
+
+    units_of_sand = 0
+    while True:
+        pos = Cell(0, 500)
+        if pos in blocked:
+            break
+
+        while True:
+            if (is_free(candidate := pos + Direction.SOUTH)) or (is_free(candidate := pos + Direction.SW)) or (is_free(candidate := pos + Direction.SE)):
+                # this unit of sand can move somewhere - move it
+                pos = candidate
+            else:
+                # this unit of sand cannot move, it has come to rest
+                blocked.add(pos)
+                units_of_sand += 1
+                break
+
+    min_col = min(c for r, c in blocked)
+    max_col = max(c for r, c in blocked)
+
+    for r in range(floor + 1):
+        print("".join("#" if (r == floor or Cell(r, c) in walls) else "o" if Cell(r, c) in blocked else "." for c in range(min_col-2, max_col+3)))
+
+    print(f"Units of sand that can come to rest (part 2): {units_of_sand}")
+
+
+
+if __name__ == "__main__":
+    part1()
+    part2()