Լայնությամբ որոնման (Breadth First Search, BFS) ալգորիթմ

from collections import deque

n, e = map(int, input().split())        # n: vertices, e: edges
g = [[] for _ in range(n)]              # graph - adjacency list

for _ in range(e):                      # read edges
    a, b = map(int, input().split())    # a -> b and b -> a
    g[a].append(b)
    g[b].append(a)

start = int(input())                    # start vertex
used = [False] * n                      # used vertices (visited)
q = deque([start])                      # queue of vertices
used[start] = True                      # mark start vertex as visited

while q:                                # while the queue is not empty
    v = q.popleft()                     # get vertex from queue
    print(v, end=' ')                   # print vertex
    for to in g[v]:                     # for each vertex connected to v
        if not used[to]:                # if vertex is not visited
            q.append(to)                # add vertex to queue
            used[to] = True             # mark vertex as visited