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48 lines
1.3 KiB
Python
48 lines
1.3 KiB
Python
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"""pseudo-code"""
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"""
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DIJKSTRA(graph G, start vertex s,destination vertex d):
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// all nodes initially unexplored
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let H = min heap data structure, initialized with 0 and s [here 0 indicates the distance from start vertex]
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while H is non-empty:
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remove the first node and cost of H, call it U and cost
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if U is not explored
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mark U as explored
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if U is d:
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return cost // total cost from start to destination vertex
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for each edge(U, V): c=cost of edge(u,V) // for V in graph[U]
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if V unexplored:
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next=cost+c
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add next,V to H (at the end)
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"""
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import heapq
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def dijkstra(graph, start, end):
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heap = [(0, start)] # cost from start node,end node
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visited = []
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while heap:
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(cost, u) = heapq.heappop(heap)
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if u in visited:
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continue
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visited.append(u)
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if u == end:
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return cost
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for v, c in G[u]:
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if v in visited:
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continue
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next = cost + c
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heapq.heappush(heap, (next, v))
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return (-1, -1)
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G = {'A': [['B', 2], ['C', 5]],
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'B': [['A', 2], ['D', 3], ['E', 1]],
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'C': [['A', 5], ['F', 3]],
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'D': [['B', 3]],
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'E': [['B', 1], ['F', 3]],
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'F': [['C', 3], ['E', 3]]}
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shortDistance = dijkstra(G, 'E', 'C')
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print(shortDistance)
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