Queue Patterns Target: 15s
Level-order BFS uses a queue with size tracking. Core pattern for tree breadth-first problems.
from collections import deque
q = deque([root])
while q:
for _ in range(len(q)):
node = q.popleft()
if node.left: q.append(node.left)
if node.right: q.append(node.right)Type it from memory. Go.