visualization

Tree BFS (Level Order)

The queue is a conveyor belt: levels go in whole, come out whole.

binary tree · root 1 · levels [1] [2,3] [4,5,6,7]step 1/16

queue (front → back)

Seed the queue with root 1. Everything BFS will ever visit flows through this queue.

pseudocode

queue = deque([root])
while queue:
    node = queue.popleft()
    visit(node)
    for child in (node.left, node.right):
        if child:
            queue.append(child)