bfs.py

graph = {
  'a' : ['b','c'],
  'b' : ['d'],
  'c' : ['e'],
  'd' : ['f'],
  'e' : [],
  'f' : []
}

visited = set() # List to keep track of visited nodes.
queue = []     #Initialize a queue

def bfs(node):
  visited.add(node)
  queue.append(node)

  while queue:
    s = queue.pop(0)
    print (s, end = " ")

    for neighbour in graph[s]:
      if neighbour not in visited:
        visited.add(node)
        queue.append(neighbour)

# Driver Code
bfs('a')

def containsX(node, target):
  pass

print(containsX('a', 'e'));