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问为什么当我运行我的程序时什么也没有发生？
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Stack Overflow用户

提问于 2017-03-09 10:08:45

回答 2查看 43关注 0票数 1

我尝试在Python中运行Dijkstra算法。但是，当我在Eclipse下执行这段代码时，什么也没有显示。我看到pydev理解了我所有的导入，并且没有错误message.Can，有人给我指出了正确的方向吗？

class Graph(object):
    def __init__(self):
        self.nodes = set()
        self.edges = {}
        self.distances = {}

    def add_node(self, value):
        self.nodes.add(value) 

    def add_edge(self, from_node, to_node, distance):
        self._add_edge(from_node, to_node, distance)
        self._add_edge(to_node, from_node, distance) 

    def _add_edge(self, from_node, to_node, distance):
        self.edges.setdefault(from_node, [])
        self.edges[from_node].append(to_node)
        self.distances[(from_node, to_node)] = distance 
def dijkstra(graph, initial_node):
    visited = {initial_node: 0}
    current_node = initial_node
    path = {}

    nodes = set(graph.nodes)

    while nodes:
        min_node = None
        for node in nodes:
            if node in visited:
                if min_node is None:
                    min_node = node
                elif visited[node] < visited[min_node]:
                    min_node = node  
        if min_node is None:
            break 

        nodes.remove(min_node)
        cur_wt = visited[min_node]

        for edge in graph.edges[min_node]:
            wt = cur_wt + graph.distances[(min_node, edge)]
            if edge not in visited or wt < visited[edge]:
                visited[edge] = wt
                path[edge] = min_node 

    return visited, path

def shortest_path(graph, initial_node, goal_node):
    distances, paths = dijkstra(graph, initial_node)
    route = [goal_node]

    while goal_node != initial_node:
        route.append(paths[goal_node])
        goal_node = paths[goal_node]

    route.reverse()
    return route

if __name__ == '__main__':
    g = Graph()
    g.nodes = set(range(1, 7))
    g.add_edge(1, 2, 7)
    g.add_edge(1, 3, 9)
    g.add_edge(1, 6, 14)
    g.add_edge(2, 3, 10)
    g.add_edge(2, 4, 15)
    g.add_edge(3, 4, 11)
    g.add_edge(3, 6, 2)
    g.add_edge(4, 5, 6)
    g.add_edge(5, 6, 9)
    assert shortest_path(g, 1, 5) == [1, 3, 6, 5]
    assert shortest_path(g, 5, 1) == [5, 6, 3, 1]
    assert shortest_path(g, 2, 5) == [2, 3, 6, 5]
    assert shortest_path(g, 1, 4) == [1, 3, 4]

python

dijkstra

回答 2

Stack Overflow用户

回答已采纳

发布于 2017-03-09 10:15:49

假设g是一个图形对象，您可以尝试打印节点、边和距离，方法如下：

print g.nodes
print g.edges
print g.distances

它将帮助您理解图形结构，并尝试使用print而不是assert。在本例中，这三行将打印以下内容：

set([1, 2, 3, 4, 5, 6])
{1: [2, 3, 6], 2: [1, 3, 4], 3: [1, 2, 4, 6], 4: [2, 3, 5], 5: [4, 6], 6:[1, 3, 5]}
{(1, 2): 7, (3, 2): 10, (1, 3): 9, (3, 6): 2, (4, 5): 6, (6, 1): 14, (3, 1): 9, (5, 4): 6, (2, 1): 7, (6, 3): 2, (5, 6): 9, (1, 6): 14, (4, 3): 11, (4, 2): 15, (2, 3): 10, (3, 4): 11, (2, 4): 15, (6, 5): 9}