88 lines
2.6 KiB
Python
88 lines
2.6 KiB
Python
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from lib import *
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from random import choice
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from collections import deque
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# def plot(graph):
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# import networkx as nx
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# import matplotlib
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# import matplotlib.pyplot as plt
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# G = nx.Graph()
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# for node, connected_nodes in graph.items():
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# for connected_node in connected_nodes:
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# G.add_edge(node, connected_node)
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# # pos = nx.spring_layout(G, k=2.0, iterations=20) # Adjust k as needed
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# pos = nx.shell_layout(G)
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# nx.draw(G, with_labels=True, node_color='lightblue', edge_color='gray', node_size=2000, font_size=15, font_weight='bold')
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# matplotlib.use('qtagg')
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# plt.show()
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def solve(input: Input):
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graph = {}
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edges = {}
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for line in input.lines():
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src, dsts = line.split(":")
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dsts = dsts.strip().split(" ")
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if not src in graph:
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graph[src] = []
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for dst in dsts:
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graph[src].append(dst)
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if not dst in graph:
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graph[dst] = []
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graph[dst].append(src)
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edge = tuple(sorted([src, dst]))
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edges[edge] = 0
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for _ in range(100):
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first_node = choice(list(graph.keys()))
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seen = set([first_node])
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visit = deque([first_node])
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while visit:
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node = visit.popleft()
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for nb in graph[node]:
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if not nb in seen:
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seen.add(nb)
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visit.append(nb)
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edge = tuple(sorted([node, nb]))
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edges[edge] += 1
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# Orignally, I used `plot(graph)` to visually find the nodes that have to
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# be removed. I then came up with this heuristic approach. The idea is that
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# we have to cross one of the three nodes when we do a breadth first
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# search. By repeatedly doing that we can identify the "bridges" as the
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# three edges that are used the most often.
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most_visited = sorted(edges.items(), key=lambda t: t[1], reverse=True)[:3]
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# to_remove = (("plt", "mgb"), ("jxm", "qns"), ("dbt", "tjd")) # found visually
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# for node, count in most_visited:
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# print(node, count) # should print the same as `to_remove`
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for (a, b), _ in most_visited:
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graph[a].remove(b)
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graph[b].remove(a)
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to_visit = [choice(list(graph.keys()))]
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seen = set(to_visit)
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while to_visit:
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node = to_visit.pop()
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for nb in graph[node]:
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if not nb in seen:
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seen.add(nb)
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to_visit.append(nb)
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return len(seen) * (len(graph) - len(seen))
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def main():
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DAY_INPUT = "d25.txt"
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print("Solution 1:", solve(Input(DAY_INPUT)), "(hands-free)")
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if __name__ == "__main__":
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main()
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