Solve 2021 day 15

2021/d15.py

@@ -0,0 +1,83 @@
+from lib import get_data
+from lib import Grid2D
+import heapq
+
+data = get_data(__file__)
+
+
+def new_data(data, repeat=5):
+    new_lines = []
+    for line in data.splitlines():
+        new_line = str(line)
+        for i in range(len(line) * repeat):
+            ni = i - len(line)
+            if ni < 0:
+                continue
+            nc = int(new_line[ni]) + 1
+            if nc == 10:
+                nc = 1
+            new_line += str(nc)
+        new_lines.append(new_line)
+
+    for i in range(len(data.splitlines()) * repeat):
+        ni = i - len(data.splitlines())
+        if ni < 0:
+            continue
+        line = list(new_lines[ni])
+        for i in range(len(line)):
+            nc = int(line[i]) + 1
+            if nc == 10:
+                nc = 1
+            line[i] = str(nc)
+        line = "".join(line)
+        new_lines.append(line)
+
+    data = "\n".join(new_lines)
+    return data
+
+
+big_data = new_data(data)
+
+for data in [data, big_data]:
+    g = Grid2D(data)
+
+    def dist(n1, n2):
+        """cost from node to node"""
+        if n1 == 0:
+            return 0
+        return int(g[n2])
+
+    def h(node):
+        """heuristic function (never overestimate)"""
+        return abs(g.n_rows - 1 - node[0]) + abs(g.n_cols - 1 - node[1])
+
+    def is_goal(node):
+        return node == (g.n_rows - 1, g.n_cols - 1)
+
+    def neighbors(node):
+        return list(g.neighbors_ort(node))
+
+    starts = [(0, 0)]
+    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))
+
+    print(cost)

README.md

@@ -186,7 +186,8 @@ Solutions and utility script for Advent of Code challenges in Python.
 - Day 12: 19:11   (Okayish, but of course too slow for leaderboard.)
 - Day 13: 16:48   (Should have been way faster.)
 - Day 14: 25:52   (Not hard but just too slow.)
-- Day 15:
+- Day 15: 19:17   (Not that bad. Multiplying the thing threw me off.)
+- Day 16:
 
 ## AoC 2022