by Pawan Kumar @jsartisan
Given a binary tree root, return its level order traversal as a nested array, where each subarray contains the values of nodes at a particular level in the tree, from left to right.
Constraints:
- 0 ≤ Number of nodes in the tree ≤ 1000
- -1000 ≤ Node values ≤ 1000
Examples:
// Example 1:
// 1
// / \
// 2 3
// / \ / \
// 4 5 6 7
const root1 = createTree([1, 2, 3, 4, 5, 6, 7]);
console.log(levelOrder(root1));
// Output: [[1], [2, 3], [4, 5, 6, 7]]
// Example 2:
// 1
const root2 = createTree([1]);
console.log(levelOrder(root2));
// Output: [[1]]
// Example 3:
const root3 = createTree([]);
console.log(levelOrder(root3));
// Output: []
// Example 4:
// 1
// / \
// 2 3
// \ \
// 4 5
const root4 = createTree([1, 2, 3, null, 4, null, 5]);
console.log(levelOrder(root4));
// Output: [[1], [2, 3], [4, 5]]
