Q60: Binary Tree Level Order Traversal. - DSA Patterns (Multi-Lang)

In Simple Words: BFS with a Queue. For each level, record levelSize = queue.length. Pop exactly levelSize nodes, collect their values in a sub-list, and push their non-null children.

Time: $O(N)$ | Space: $O(W) = O(N)$

Multi-Language SolutionsPython 3 • JavaScript • TypeScript • Java • C++

Switch tabs or choose All

from collections import deque

def levelOrder(root: TreeNode | None) -> list[list[int]]:
    if not root: return []
    res = []
    q = deque([root])
    while q:
        level = []
        for _ in range(len(q)):
            node = q.popleft()
            level.append(node.val)
            if node.left: q.append(node.left)
            if node.right: q.append(node.right)
        res.append(level)
    return res