"""pseudo-code"""
"""
BFS(graph G, start vertex s):
// all nodes initially unexplored
mark s as explored
let Q = queue data structure, initialized with s
while Q is non-empty:
remove the first node of Q, call it v
for each edge(v, w): // for w in graph[v]
if w unexplored:
mark w as explored
add w to Q (at the end)
"""
import collections
def bfs(graph, start):
explored, queue = set(), [start] # collections.deque([start])
explored.add(start)
while queue:
v = queue.pop(0) # queue.popleft()
for w in graph[v]:
if w not in explored:
explored.add(w)
queue.append(w)
return explored
G = {'A': ['B', 'C'],
'B': ['A', 'D', 'E'],
'C': ['A', 'F'],
'D': ['B'],
'E': ['B', 'F'],
'F': ['C', 'E']}
print(bfs(G, 'A'))