在python中实现bfs算法

Question

I have written this piece of code to start a bfs traversal from element x in a given graph(from input) and finally print the number of visited vertices. but it doesn't work.:( for example for the below input,the right output is 6 but my code prints 3. input:

6
1 2
1 3
2 4
3 5
3 6
4 6

python code

from collections import defaultdict

def make_graph(graph,u,v):
    graph[u].append(v)
def bfs(visited, graph, node):
    output=[]
    visited.append(node)
    queue.append(node)
    while queue:
        node = queue.pop(0)
        output.append(node)
        for nghbr in graph[node]:
            if nghbr not in visited:
                visited.append( nghbr )
                queue.append( nghbr )
    print(len(output))

x='3'
#bfs starts from node x in graph
n=int(input())
#n:number of nodes(number of nodes is equal to number of edges)
graph = defaultdict(list)
visited=[]
queue = []
for i in range (n):
    u,v=input().split()
    make_graph(graph,u,v)

bfs(visited, graph,x)

Answer 1

There are few issuses here:

1. You are using the defaultdict class from the collections module to create a dictionary where all the keys have an empty list as their default value. However, you are adding the keys to the dictionary as strings, but you are using them as integers when you call the bfs function.
2. You are not adding the edges to the graph correctly.
3. You are using the variable queue to store the nodes to visit, but you are not initializing it before using it.