Binary Tree Reverse Level Order Traversal- LeetCode: Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

ReverseBinaryTreeTraversal2.java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<List<Integer>> levelOrderBottom(TreeNode root) {
          List<List<Integer>> result = new ArrayList<>();
        if(root == null){
            return result;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while(!queue.isEmpty()){
            List<Integer> temRes = new ArrayList<>();
            for(TreeNode node : queue){
                temRes.add(node.val);
                
            }
            result.add(temRes);
            queue = makeQueue(queue);
           
        }
        Collections.reverse(result);
        return result;
    }
   
    Queue<TreeNode> makeQueue(Queue<TreeNode> queue){
        Queue<TreeNode> queueCopy = new LinkedList<>();
        while(!queue.isEmpty()){
            TreeNode treeNode = queue.remove();
            if(treeNode.left != null)
                queueCopy.add(treeNode.left);
            if(treeNode.right != null)
                queueCopy.add(treeNode.right);
        }
        return queueCopy;
        
    }
}