在 python 中使用 BFS 的未加权单源最短路径

Question

我是 python 的新人。我尝试使用 BFS 获取 Unweighted-Single-Source-Shortest-Path。

from queue import *


def ussp(graph, s):
    len_graph = len(graph)
    prev = [[]*len_graph for i in range(len_graph)]
    visited = [False for i in range(len_graph)]
    queue2 = Queue
    dist = [[float('inf')] for i in range(len_graph)]
    queue2.put_nowait(graph[s], 0)  # starting with s
    visited[s] = True
    dist[s] = 0

    # modified BFS alg.
    while queue2.empty() == False:
        h = queue2.get_nowait()
        for i in len(graph[h]):
            if visited[graph[h][i]] == False:
                visited[graph[h][i]] = True
                dist[graph[h][i]] = dist[h] + 1
                prev[graph[h][i]] = h
                queue2.put_nowait(graph[h][i], 0)
    print(dist)


graph2 = {1: [2, 3, 5], 2: [4, 6, 1], 3: [5, 1], 4: [6], 5: [2], 6: [1, 7], 7: [2]}
ussp(graph2, 1)

这就是我现在得到的。我很确定它应该工作，但它根本没有。它甚至没有被编译。我对 python 中的列表、数组和队列也很陌生。如果你能帮助我，我将不胜感激。提前致谢

Answer 1

这一行是您出错的原因：

queue2 = Queue

您将 queue2 设置为等于 Queue class，而不是 Queue class.

的实例

将该行更改为：

queue2 = Queue()

Answer 2

首先，我在您的函数签名中添加了一个目标参数。假设您想找到从节点 1 到节点 7 的最短路径，下面的程序可以运行。我还添加了一些 python 样板，因为你说你是 python.

的新手

import sys
from queue import Queue as Q

def ussp(graph, s, d):
    len_graph = len(graph)

    prev = [ -1 for i in range(len_graph)]
    visited = [False for i in range(len_graph)]
    q = Q()
    dist = [sys.maxsize for i in range(len_graph)]
    q.put(s, False)
    visited[s-1] = True
    dist[s-1] = 0

    # modified BFS alg.
    while q.empty() == False:
        h = q.get_nowait()
        for i in range(len(graph[h])):
            if visited[graph[h][i]-1] == False:
                visited[graph[h][i]-1] = True
                dist[graph[h][i]-1] = dist[h-1] + 1
                prev[graph[h][i]-1] = h
                q.put_nowait(graph[h][i])

    path = []
    crawl = d # destination
    path.append(crawl)
    while (prev[crawl-1] != -1):
        path.append(prev[crawl-1])
        crawl = prev[crawl-1]

    print(list(reversed(path)))


def main():
    graph2 = {1: [2, 3, 5], 2: [4, 6, 1], 3: [5, 1], 4: [6], 5: [2], 6: [1, 7], 7: [2]}
    ussp(graph2, 1, 7)

if __name__ == '__main__':
    main()

在 python 中使用 BFS 的未加权单源最短路径

Unweighted-Single-Source-Shortest-Path using BFS in python

python

shortest-path

breadth-first-search