Add solution to 2024-12-20

Author: fuglede

2024/day20/solutions.py

@@ -0,0 +1,31 @@
+from itertools import combinations
+
+import networkx as nx
+
+with open("input") as f:
+    ls = f.read().strip().split("\n")
+
+G = nx.grid_2d_graph(len(ls), len(ls[0]))
+for i, l in enumerate(ls):
+    for j, x in enumerate(l):
+        p = (i, j)
+        if x == "#":
+            G.remove_node(p)
+        elif x == "S":
+            start = p
+
+dist = nx.single_source_dijkstra_path_length(G, start)
+
+
+def solve(cheat_dist):
+    return sum(
+        (d := abs(p1 - q1) + abs(p2 - q2)) <= cheat_dist and d2 - d1 - d >= 100
+        for ((p1, p2), d1), ((q1, q2), d2) in combinations(dist.items(), 2)
+    )
+
+
+# Part 1
+print(solve(2))
+
+# Part 2
+print(solve(20))