迪克斯特拉算法python实现

Posted 2021-01-05 masterhu

graph={}
graph[‘start‘]={}        #定义图中的各个邻居节点
graph[‘start‘][‘a‘]=6
graph[‘start‘][‘b‘]=-1
graph[‘a‘]={}
graph[‘a‘][‘end‘]=1
graph[‘b‘]={}
graph[‘b‘][‘a‘]=3
graph[‘b‘][‘end‘]=5
graph[‘end‘]={}
cost={}             #首尾已知点的代价
infinity=float(‘inf‘)
cost[‘a‘]=6
cost[‘b‘]=-1
cost[‘end‘]=infinity
parent={}         #首尾已知点的负节点
parent[‘a‘]=‘start‘
parent[‘b‘]=‘start‘
parent[‘end‘]=None
#print(cost.keys())
process=[]
def select_lowest_cost(cost):
    lowest_cost=float(‘inf‘)
    lowest_cost_node=None
    for node in cost.keys() :
        if cost[node]<lowest_cost and node not in process:    #保证所有的初始节点（第一步）都被考虑到
            lowest_cost=cost[node]
            lowest_cost_node=node
    return lowest_cost_node
#print(select_lowest_cost(cost))
node=select_lowest_cost(cost)
while node is not None:
    neighbor=graph[node]
    costs=cost[node]
    #neighbor[node]=graph[node].keys()
    for i in neighbor.keys():
        c=costs+neighbor[i]
        if c<cost[i]:
            cost[i]=c
            parent[i]=node
    process.append(node)        #处理完的点表示该节点所有的邻居节点都考虑完全
    node = select_lowest_cost(cost)
print(cost[‘end‘])