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41 lines
1.1 KiB
Python
41 lines
1.1 KiB
Python
"""pseudo-code"""
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"""
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DFS(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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for every edge (s, v):
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if v unexplored:
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DFS(G, v)
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"""
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def dfs(graph, start):
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"""The DFS function simply calls itself recursively for every unvisited child of its argument. We can emulate that
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behaviour precisely using a stack of iterators. Instead of recursively calling with a node, we'll push an iterator
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to the node's children onto the iterator stack. When the iterator at the top of the stack terminates, we'll pop
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it off the stack."""
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explored, stack = set(), [start]
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while stack:
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v = stack.pop() # one difference from BFS is to pop last element here instead of first one
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if v in explored:
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continue
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explored.add(v)
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for w in graph[v]:
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if w not in explored:
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stack.append(w)
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return explored
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G = {'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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print(dfs(G, 'A'))
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