Solve 2024 till day 18

2024/d18.py

@@ -0,0 +1,67 @@
+import heapq
+from lib import get_data
+from lib import ints
+from lib import Grid2D
+
+data = get_data(__file__)
+
+size = 71
+grid = "\n".join(["." * size for _ in range(size)])
+
+g = Grid2D(grid)
+for i, line in enumerate(data.splitlines()):
+    x, y = ints(line)
+    g[(y, x)] = "x"
+
+    start = (0, 0)
+    end = (size - 1, size - 1)
+
+    def dist(n1, n2):
+        """cost from node to node"""
+        if n1 == 0 or n1 == n2:
+            return 0
+        return 1
+
+    def h(node):
+        """heuristic function (never overestimate)"""
+        return abs(node[0] - end[0]) + abs(node[1] - end[1])
+
+    def is_goal(node):
+        return node == end
+
+    def neighbors(node):
+        nbs = []
+        for nb in g.neighbors_ort(node):
+            if g[nb] != "x":
+                nbs.append(nb)
+        return nbs
+
+    starts = [start]
+    open_set = []
+    g_score = {}
+    cost = None
+
+    for start in starts:
+        heapq.heappush(open_set, (h(start), start))
+        g_score[start] = dist(0, start)
+
+    while open_set:
+        current_f_score, current = heapq.heappop(open_set)
+        if is_goal(current):
+            assert current_f_score == g_score[current]
+            cost = g_score[current]
+            break
+
+        for neighbor in neighbors(current):
+            tentative_g_score = g_score[current] + dist(current, neighbor)
+            if neighbor not in g_score or tentative_g_score < g_score[neighbor]:
+                g_score[neighbor] = tentative_g_score
+                f_score = g_score[neighbor] + h(neighbor)
+                heapq.heappush(open_set, (f_score, neighbor))
+
+    if i == 1023:
+        print(cost)
+
+    if cost is None:
+        print(line)
+        break