Binary Tree Right Side View

for self practice

Given the root of a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

 

Example 1:

Input: root = [1,2,3,null,5,null,4]
Output: [1,3,4]

Example 2:

Input: root = [1,null,3]
Output: [1,3]

Example 3:

Input: root = []
Output: []

 

Constraints:

• The number of nodes in the tree is in the range [0, 100].
• -100 <= Node.val <= 100

package practice;
import java.util.*;

public class BinaryTreeRightSideView {

    //https://leetcode.com/problems/binary-tree-right-side-view/solution/

    public List<Integer> rightSideView(TreeNode root) {

        if (root == null) return new ArrayList<Integer>();
        List<Integer> list=new ArrayList<>();
        Queue<TreeNode> queue=new LinkedList<>();
        queue.offer(root);

        while(!queue.isEmpty()){
            int levelsize=queue.size();
            for(int i=0; i<levelsize; i++){
                TreeNode node=queue.poll();
                if(i==(levelsize-1)){
                    list.add(node.val);
                }

                if(node.left!=null){
                    queue.offer(node.left);
                }

                if(node.right!=null){
                    queue.offer(node.right);
                }
            }
        }
        return list;
    }
}