Tree Traversal Target: 15s
Level-order collects node values per level. Foundation for zigzag and right-side-view.
from collections import deque
q = deque([root])
res = []
while q:
lvl = []
for _ in range(len(q)):
n = q.popleft()
lvl.append(n.val)
if n.left: q.append(n.left)
if n.right: q.append(n.right)
res.append(lvl)Type it from memory. Go.