[GeeksForGeeks] Print leftmost and rightmost nodes at each level of a binary tree.

 1 import java.util.ArrayList;
 2 import java.util.LinkedList;
 3 import java.util.Queue;
 4 
 5 class TreeNode {
 6     TreeNode left;
 7     TreeNode right;
 8     int val;
 9     TreeNode(int val){
10         this.left = null;
11         this.right = null;
12         this.val = val;
13     }
14 }
15 public class Solution {
16     public ArrayList<TreeNode> getLeftRightMostAtEachLevel(TreeNode root) {
17         ArrayList<TreeNode> result = new ArrayList<TreeNode>();
18         if(root == null){
19             return result;
20         }
21         Queue<TreeNode> queue = new LinkedList<TreeNode>();
22         queue.offer(root);        
23         while(!queue.isEmpty()){
24             int size = queue.size();
25             for(int i = 0; i < size; i++){
26                 TreeNode curr = queue.poll();
27                 if(i == 0){
28                     result.add(curr);
29                 }
30                 if(i > 0 && i == size - 1){
31                     result.add(curr);
32                 }
33                 if(curr.left != null){
34                     queue.offer(curr.left);
35                 }
36                 if(curr.right != null){
37                     queue.offer(curr.right);
38                 }
39             }
40         }
41         return result;
42     }
43 }