Binary Tree Level Order Traversal
Given the root of a binary tree, return the level order traversal of its nodes' values, from left to right and level by level.
Example 1
3
/ \
9 20
/ \
15 7Input
root = [3,9,20,null,null,15,7]Output
[[3],[9,20],[15,7]]The traversal visits the root first, then the second level from left to right, then the third level from left to right.
Example 2
1
Input
root = [1]Output
[[1]]The tree has only one node, so the traversal contains one level with that value.
Constraints
- The number of nodes in the tree is in the range
[0, 2000]. -1000 <= Node.val <= 1000
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