Solve day 25. Only d21 part 2 left o.O

README.md

@@ -2,10 +2,9 @@ My solutions to the Advent of Code 2023 programming challenges.
 
 Thanks to Eric Wastl for creating this enjoyable event.
 
-Requires `lib.py` from [aocpy](https://git.felixm.de/felixm/aocpy) repository.
-
-Requires `sympy` for day 24.
-
+- Requires `lib.py` from [aocpy](https://git.felixm.de/felixm/aocpy) repository.
+- Requires `sympy` for day 24.
+- Requires `matplotlib` and `networkx` for hands-on day 25.
 
 # Times
 
@@ -40,11 +39,15 @@ Requires `sympy` for day 24.
   the input conjunction gate pretty early, but then messed up the
   implementation and thought it wasn't gonna work. Spent a half day thinking up
   something else before returning to the idea and it worked flawlessly.
-- Day 21:
+- Day 21: Part 1 was straightforward, but part 2 maybe the hardest problem this
+  year.
 - Day 22: Not too hard, but definitely way too slow for leaderboard.
 - Day 23: I found this fun because it required some creativity for part 2. Slow
   af, of course.
-- Day 24: Solve problem with sympy. I first used numpy to solve part 1 and it was
-  much faster than using sympy, but I lost that solution when switching to sympy.
-  Takes about three minutes to run for part 1 and then part 2 is under a second.
-- Day 25:
+- Day 24: Solve problem with sympy. I first used numpy to solve part 1 and it
+  was much faster than using sympy, but I lost that solution when switching to
+  sympy. Takes about three minutes to run for part 1 and then part 2 is under a
+  second.
+- Day 25: I cheeky solved this by plotting the graph and manually removing the
+  nodes. I should probably try to write an algorith that does that, but meh.
+  Manually plotting requires matplotlib and networkx packages.

d25.py

@@ -0,0 +1,60 @@
+from lib import *
+
+
+def plot(graph):
+    import networkx as nx
+    import matplotlib
+    import matplotlib.pyplot as plt
+    G = nx.Graph()
+    for node, connected_nodes in graph.items():
+        for connected_node in connected_nodes:
+            G.add_edge(node, connected_node)
+    # pos = nx.spring_layout(G, k=2.0, iterations=20)  # Adjust k as needed
+    pos = nx.shell_layout(G)
+    nx.draw(G, with_labels=True, node_color='lightblue', edge_color='gray', node_size=2000, font_size=15, font_weight='bold')
+    matplotlib.use('qtagg')
+    plt.show()
+
+
+def solve_non_hands_free(input: Input, second=False):
+    graph = {}
+    for line in input.lines():
+        source, targets = line.split(":")
+        targets = targets.strip()
+        targets = targets.split(" ")
+
+        for target in targets:
+            if not source in graph:
+                graph[source] = [target]
+            else:
+                graph[source].append(target)
+            if not target in graph:
+                graph[target] = [source]
+            else:
+                graph[target].append(source)
+
+    # plot(graph) # I used this to find the nodes that have to be removed.
+    to_remove = (("plt", "mgb"), ("jxm", "qns"), ("dbt", "tjd"))
+    for a, b in to_remove:
+        graph[a].remove(b)
+        graph[b].remove(a)
+
+    to_visit = ["plt"]
+    seen = set(to_visit)
+    while to_visit:
+        node = to_visit.pop()
+        for nb in graph[node]:
+            if not nb in seen:
+                seen.add(nb)
+                to_visit.append(nb)
+
+    return len(seen) * (len(graph) - len(seen))
+
+
+def main():
+    DAY_INPUT = "i25.txt"
+    print("Solution 1:", solve_non_hands_free(Input(DAY_INPUT)))
+
+
+if __name__ == "__main__":
+    main()