mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-11-28 07:21:07 +00:00
48 lines
1.3 KiB
Python
48 lines
1.3 KiB
Python
|
"""pseudo-code"""
|
||
|
|
|
||
|
|
"""
|
||
|
|
DIJKSTRA(graph G, start vertex s,destination vertex d):
|
||
|
|
// all nodes initially unexplored
|
||
|
|
let H = min heap data structure, initialized with 0 and s [here 0 indicates the distance from start vertex]
|
||
|
|
while H is non-empty:
|
||
|
|
remove the first node and cost of H, call it U and cost
|
||
|
|
if U is not explored
|
||
|
|
mark U as explored
|
||
|
|
if U is d:
|
||
|
|
return cost // total cost from start to destination vertex
|
||
|
|
for each edge(U, V): c=cost of edge(u,V) // for V in graph[U]
|
||
|
|
if V unexplored:
|
||
|
|
next=cost+c
|
||
|
|
add next,V to H (at the end)
|
||
|
|
"""
|
||
|
|
import heapq
|
||
|
|
|
||
|
|
|
||
|
|
def dijkstra(graph, start, end):
|
||
|
|
heap = [(0, start)] # cost from start node,end node
|
||
|
|
visited = []
|
||
|
|
while heap:
|
||
|
|
(cost, u) = heapq.heappop(heap)
|
||
|
|
if u in visited:
|
||
|
|
continue
|
||
|
|
visited.append(u)
|
||
|
|
if u == end:
|
||
|
|
return cost
|
||
|
|
for v, c in G[u]:
|
||
|
|
if v in visited:
|
||
|
|
continue
|
||
|
|
next = cost + c
|
||
|
|
heapq.heappush(heap, (next, v))
|
||
|
|
return (-1, -1)
|
||
|
|
|
||
|
|
|
||
|
|
G = {'A': [['B', 2], ['C', 5]],
|
||
|
|
'B': [['A', 2], ['D', 3], ['E', 1]],
|
||
|
|
'C': [['A', 5], ['F', 3]],
|
||
|
|
'D': [['B', 3]],
|
||
|
|
'E': [['B', 1], ['F', 3]],
|
||
|
|
'F': [['C', 3], ['E', 3]]}
|
||
|
|
|
||
|
|
shortDistance = dijkstra(G, 'E', 'C')
|
||
|
|
print(shortDistance)
|