MediumTrees
Binary Tree Level Order Traversal
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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).
Example 1:
3
/ \
9 20
/ \
15 7
Input: root = [3,9,20,null,null,15,7]
Output: [[3],[9,20],[15,7]]
Example 2:
Input: root = [1]
Output: [[1]]
Example 3:
Input: root = []
Output: []
Examples
Example 1
Input: root = [3,9,20,null,null,15,7]
Output: [[3],[9,20],[15,7]]
Explanation: Level 0 contains just the root [3]. Level 1 contains [9, 20]. Level 2 contains [15, 7] (children of 20).
Example 2
Input: root = [1,2,3,4,5]
Output: [[1],[2,3],[4,5]]
Explanation: Level 0: [1]. Level 1: [2, 3]. Level 2: [4, 5] (children of 2).
Constraints
- -The number of nodes in the tree is in the range [0, 2000].
- --1000 <= Node.val <= 1000
Optimal Complexity
Time
O(n)
Space
O(n)
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