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37 lines
1.0 KiB
Python
37 lines
1.0 KiB
Python
"""Topological Sort."""
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from __future__ import print_function
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# a
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# / \
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# b c
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# / \
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# d e
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edges = {'a': ['c', 'b'], 'b': ['d', 'e'], 'c': [], 'd': [], 'e': []}
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vertices = ['a', 'b', 'c', 'd', 'e']
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def topological_sort(start, visited, sort):
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"""Perform topolical sort on a directed acyclic graph."""
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current = start
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# add current to visited
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visited.append(current)
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neighbors = edges[current]
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for neighbor in neighbors:
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# if neighbor not in visited, visit
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if neighbor not in visited:
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sort = topological_sort(neighbor, visited, sort)
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# if all neighbors visited add current to sort
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sort.append(current)
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# if all vertices haven't been visited select a new one to visit
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if len(visited) != len(vertices):
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for vertice in vertices:
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if vertice not in visited:
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sort = topological_sort(vertice, visited, sort)
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# return sort
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return sort
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if __name__ == '__main__':
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sort = topological_sort('a', [], [])
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print(sort)
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