Competitive-Programming/July LeetCode Challenge/2. Binary Tree Level Order Traversal II/Solution.java at master · rohitkumar-rk/Competitive-Programming · GitHub

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/*
@lc id : 107 Binary Tree Level Order Traversal II
Author : Rohit
Date : 02/07/2020
*/

class Solution {
    public List<List<Integer>> levelOrderBottom(TreeNode root) {

        if(root == null)
            return new ArrayList<List<Integer>>();

        Queue<TreeNode> queue = new  LinkedList<TreeNode>();
        List<List<Integer>> levelOrderTraversal = new ArrayList<List<Integer>>();
        queue.add(root);

        while(!queue.isEmpty()){
            int qSize = queue.size();
            List<Integer> currLevel = new ArrayList<Integer>();

            for(int i = 0; i < qSize; i++){
                TreeNode currNode = queue.remove();
                currLevel.add(currNode.val);

                if(currNode.left != null)
                    queue.add(currNode.left);

                if(currNode.right != null)
                    queue.add(currNode.right);
            }

            levelOrderTraversal.add(0, currLevel);
        }

        return levelOrderTraversal;

    }
}