在python中使用BFS的Unweighted-Single-Source-Shortest-Path

Question

我是python的新手。 我嘗試使用BFS獲得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)

那就是我現在得到的。 我非常確定它應該可以工作，但是根本不起作用。 它甚至沒有被編譯。 我在python中使用列表，數組和隊列也很新。 如果您能幫助我，會很高興。 提前致謝

Answer 1

首先，我在函數簽名中添加了一個目標參數。 假設您想找到從節點1到節點7的最短路徑，下面的程序將起作用。 我還添加了一些python樣板，因為您說過您是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()

Answer 2

此行是導致您出錯的原因：

queue2 = Queue

你設置queue2等於Queue ，而不是一個實例類， Queue類。

將該行更改為此：

queue2 = Queue()