Reverse Level Order Traversal

Traverse a given binary tree in the Reverse Level Order. Mark a node as visited by adding its data to an ArrayList which will be returned.

Example:  
     1
    / \
   2   3     
  / \ / \
 4  5 6  7 

Output => 4567231

Need a hand? Try out these hints, one at a time.

Reverse Levelorder Traversal : traverse the tree starting from the lowest level up. At each level, read the nodes from left to right.

Use a Queue to traverse through the nodes at each level and use a Stack to read the nodes in the reverse order.

1. If root is null, return.

2. Declare a Queue and a Stack.

3. Queue the root.

4. Loop while the Queue is not empty.

5. Within the loop, dequeue a node and insert its left and right nodes into the Queue. At the same time, push this element onto the Stack.

6. Once the loop completes, pop the Stack's elements one by one and add them to the ArrayList.

public ArrayList<Integer> levelorderRev(TreeNode root) { 
                       





    
}

Java

Python