Binary Tree Level Order Traversal
Medium
Tree
Breadth-First Search
Binary Tree
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
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: []

Constraints

  • •The number of nodes in the tree is in the range [0, 2000].
  • •-1000 <= Node.val <= 1000
Time Complexity
O(n)
Space Complexity
O(n)
14
Case 1
Input: [3,9,20,null,null,15,7]
Expected: [[3],[9,20],[15,7]]
Case 2
Input: [1]
Expected: [[1]]
Case 3
Input: []
Expected: []