You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
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def graph_topo_sort(num_nodes, edges):
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from collections import deque
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nodes, order, queue = {}, [], deque()
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for node_id in range(num_nodes):
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nodes[node_id] = { 'in': 0, 'out': set() }
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for node_id, pre_id in edges:
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nodes[node_id]['in'] += 1
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nodes[pre_id]['out'].add(node_id)
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for node_id in nodes.keys():
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if nodes[node_id]['in'] == 0:
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queue.append(node_id)
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while len(queue):
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node_id = queue.pop()
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for outgoing_id in nodes[node_id]['out']:
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nodes[outgoing_id]['in'] -= 1
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if nodes[outgoing_id]['in'] == 0:
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queue.append(outgoing_id)
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order.append(node_id)
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return order if len(order) == num_nodes else None
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print(graph_topo_sort(4, [[0, 1], [0, 2], [2, 1], [3, 0]]))
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# [1, 2, 0,3 ]
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