33 lines
669 B
Python
33 lines
669 B
Python
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import fileinput
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from collections import defaultdict
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def build_graph():
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graph = defaultdict(list)
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for line in fileinput.input():
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a, b = line[5], line[36]
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graph[b].append(a)
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graph[a]
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return graph
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def main():
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graph = build_graph()
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order = []
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to_consider = sorted(graph.keys())
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while to_consider:
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for i, node in enumerate(to_consider):
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parents = graph[node]
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if any(parent in to_consider for parent in parents):
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continue
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order.append(node)
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del to_consider[i]
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break
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print("".join(order))
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if __name__ == "__main__":
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main()
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