102. Binary Tree Level Order Traversal

Given the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level).



def levelOrder(root):
   
    res = {}
    if root is None:
        return res
    q = deque()
    q.append((root, 0))

    while q:
        n, level = q.popleft()
        if level not in res:
            res[level] = []
        res[level].append(n.val)
                   
        if n.left:
            q.append((n.left, level+1))
        if n.right:
            q.append((n.right, level+1))
                   
    return res.values()

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