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e6cf13cc03
* Update queue implementation Popping the first element of a list takes O(n) time. Using a cyclic queue takes O(1) time. * Add queue changes from extra files * Update indentation * Add empty line between imports * Fix lines * Apply suggestions from code review Co-authored-by: John Law <johnlaw.po@gmail.com> Co-authored-by: John Law <johnlaw.po@gmail.com>
48 lines
1.1 KiB
Python
48 lines
1.1 KiB
Python
"""
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https://en.wikipedia.org/wiki/Breadth-first_search
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pseudo-code:
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breadth_first_search(graph G, start vertex s):
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// all nodes initially unexplored
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mark s as explored
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let Q = queue data structure, initialized with s
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while Q is non-empty:
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remove the first node of Q, call it v
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for each edge(v, w): // for w in graph[v]
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if w unexplored:
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mark w as explored
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add w to Q (at the end)
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"""
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from __future__ import annotations
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from queue import Queue
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G = {
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"A": ["B", "C"],
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"B": ["A", "D", "E"],
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"C": ["A", "F"],
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"D": ["B"],
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"E": ["B", "F"],
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"F": ["C", "E"],
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}
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def breadth_first_search(graph: dict, start: str) -> set[str]:
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"""
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>>> ''.join(sorted(breadth_first_search(G, 'A')))
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'ABCDEF'
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"""
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explored = {start}
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queue = Queue()
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queue.put(start)
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while not queue.empty():
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v = queue.get()
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for w in graph[v]:
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if w not in explored:
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explored.add(w)
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queue.put(w)
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return explored
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if __name__ == "__main__":
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print(breadth_first_search(G, "A"))
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