 Just like with Tree BFS, we can get Graph BFS code by simply taking the preorder /coding/143, Iterative Tree DFS code , and swapping out the stack with a queue. And now that we're on a Graph, we need to keep track of the nodes we've visited so we don't enter an infinite cycle. ``` A queue of all the nodes we want to call visitAll() on. queue = deque([root]) visited_nodes = set() while queue: take a node off the queue and visit it node = queue.popleft() if node in visited_nodes: continue visited

Graph BFS


\image{2}

Just like with Tree BFS, we can get Graph BFS code by simply taking the preorder \link{/coding/143, Iterative Tree DFS code}, and swapping out the stack with a queue. And now that we're on a Graph, we need to keep track of the nodes we've visited so we don't enter an infinite cycle. 


```
# A queue of all the nodes we want to call visitAll() on.
queue = deque([root])
visited_nodes = set() 
while queue:

    # take a node off the queue and visit it
    node = queue.popleft() 

    if node in visited_nodes: 
        continue
    visited_nodes.add(node)

    do_something(node) 

    for nbr in node.neighbors:
        queue.append(nbr)

```


Recursion

Graph BFS