Solve 2018 day 13

2018/d13.py

@@ -0,0 +1,102 @@
+from lib import Grid2D, add2
+
+CARTS = (
+    ("^", Grid2D.N, "|"),
+    ("v", Grid2D.S, "|"),
+    (">", Grid2D.E, "-"),
+    ("<", Grid2D.W, "-"),
+)
+TURNS = "lsr"
+DIRS = [(-1, 0), (0, 1), (1, 0), (0, -1)]
+
+
+def part_1(data):
+    g = Grid2D(data)
+    first_shown = False
+    carts = []
+    occupied = set()
+
+    for c, d, r in CARTS:
+        for cart in g.find(c):
+            carts.append((cart, d, "l"))
+            g[cart] = r
+            occupied.add(cart)
+
+    for _ in range(1, 100_000):
+        carts = sorted(carts)
+
+        ncarts = []
+        i_to_skip = []
+        for i in range(len(carts)):
+            if i in i_to_skip:
+                continue
+
+            pos, dir, turn = carts[i]
+            occupied.remove(pos)
+            pos = add2(pos, dir)
+
+            # detect collision and remove carts
+            if pos in occupied:
+                if first_shown is False:
+                    print(f"{pos[1]},{pos[0]}")
+                    first_shown = True
+                # either from carts that haven't moved, yet
+                for j in range(len(carts)):
+                    jpos, _, _ = carts[j]
+                    if jpos == pos:
+                        i_to_skip.append(j)
+                        break
+                else:
+                    # or from carts that have already moved
+                    ncarts = list(filter(lambda c: c[0] != pos, ncarts))
+                occupied.remove(pos)
+                continue
+            else:
+                occupied.add(pos)
+
+            if g[pos] == "+":
+                if turn == "l":
+                    dir = DIRS[(DIRS.index(dir) - 1) % len(DIRS)]
+                elif turn == "r":
+                    dir = DIRS[(DIRS.index(dir) + 1) % len(DIRS)]
+                turn = TURNS[(TURNS.index(turn) + 1) % len(TURNS)]
+            elif g[pos] == "/":
+                if dir == g.E:
+                    dir = g.N
+                elif dir == g.W:
+                    dir = g.S
+                elif dir == g.N:
+                    dir = g.E
+                elif dir == g.S:
+                    dir = g.W
+                else:
+                    assert False
+            elif g[pos] == "\\":
+                if dir == g.E:
+                    dir = g.S
+                elif dir == g.W:
+                    dir = g.N
+                elif dir == g.N:
+                    dir = g.W
+                elif dir == g.S:
+                    dir = g.E
+                else:
+                    assert False
+
+            ncarts.append((pos, dir, turn))
+        carts = ncarts
+        if len(carts) == 1:
+            pos = carts[0][0]
+            print(f"{pos[1]},{pos[0]}")
+            return
+
+
+def main():
+    input_file = __file__.replace(".py", ".txt")
+    with open(input_file) as f:
+        data = f.read()
+    part_1(data)
+
+
+if __name__ == "__main__":
+    main()

README.md

@@ -101,7 +101,8 @@ written in Python.
 - Day 10: 19:14
 - Day 11: 22:52
 - Day 12: 180:00
-- Day 13:
+- Day 13: 73:09
+- Day 14:
 
 
 # 2022