Given a binary tree, find its level order traversal.
Level order traversal of a tree is breadth-first traversal for the tree.
Output:1 3 2
Output:10 20 30 40 60 N N
Your Task: You don't have to take any input. Complete the function levelOrder() that takes the root node as input parameter and returns a list of integers containing the level order traversal of the given Binary Tree.
Expected Time Complexity: O(N) Expected Auxiliary Space: O(N)
1 <= Number of nodes<= 104
1 <= Data of a node <= 104