D算法代码实现

旧城等待， 2022-05-18 02:24 203阅读 0赞

D算法用于搜索起始点到终点或其他各点的最短路径和距离

D算法不能应用于包含负权变的图

D算法求解步骤：

初始化起始点到其他各个点的距离

循环：直到未处理节点为空

在未处理过的点中选择与起始点距离最小的点

计算初始结点经选定点转接后与选定点的邻居节点的距离，若距离更短则更新距离和路由

将该选定的节点标记为已处理点

# the graph
    graph = {}
    graph["start"] = {}
    graph["start"]["a"] = 6
    graph["start"]["b"] = 2
    
    graph["a"] = {}
    graph["a"]["fin"] = 1
    
    graph["b"] = {}
    graph["b"]["a"] = 3
    graph["b"]["fin"] = 5
    
    graph["fin"] = {}
    
    # the costs table
    infinity = float("inf")
    costs = {}
    costs["a"] = 6
    costs["b"] = 2
    costs["fin"] = infinity
    
    # the parents table
    parents = {}
    parents["a"] = "start"
    parents["b"] = "start"
    parents["fin"] = None
    
    processed = []
    
    def find_lowest_cost_node(costs):
        lowest_cost = float("inf")
        lowest_cost_node = None
        # Go through each node.
        for node in costs:
            cost = costs[node]
            # If it's the lowest cost so far and hasn't been processed yet...
            if cost < lowest_cost and node not in processed:
                # ... set it as the new lowest-cost node.
                lowest_cost = cost
                lowest_cost_node = node
        return lowest_cost_node
    
    # Find the lowest-cost node that you haven't processed yet.
    node = find_lowest_cost_node(costs)
    # If you've processed all the nodes, this while loop is done.
    while node is not None:
        cost = costs[node]
        # Go through all the neighbors of this node.
        neighbors = graph[node]#邻居节点中存储邻居节点和他到邻居节点的距离
        for n in neighbors.keys():#遍历整个邻居节点，更新转接距离和路由
            new_cost = cost + neighbors[n]
            # If it's cheaper to get to this neighbor by going through this node...
            if costs[n] > new_cost:
                # ... update the cost for this node.
                costs[n] = new_cost
                # This node becomes the new parent for this neighbor.
                parents[n] = node
        # Mark the node as processed.
        processed.append(node)
        # Find the next node to process, and loop.
        node = find_lowest_cost_node(costs)
    
    print "Cost from the start to each node:"
    print costs