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).

class Solution:
    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
        if not root:
            return []
        
        levels = []
        
        q = deque([root])
        
        while q:
            len_level = len(q)
            levels.append([x.val for x in q])
            
            for _ in range(len_level):
                cur = q.popleft()
                if cur.left: q.append(cur.left)
                if cur.right: q.append(cur.right)
        return levels

• do a standard bfs while keeping track of levels.
• append the levels to a output array.

Categories:: array, bfs, binary-tree, tree