/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode() {}

* TreeNode(int val) { this.val = val; }

* TreeNode(int val, TreeNode left, TreeNode right) {

* this.val = val;

* this.left = left;

* this.right = right;

* }

* }

*/

class Solution {

public List<Integer> rightSideView(TreeNode root) {

// idea -

// in order to have the right side view, needs to know each level, and to know

// the most right side element, and this calls for a bfs method.

// to keep track of elements on that level, a level is also tracked

// a map is used to update the element on the right hand side

Queue<TreeNode> q = new LinkedList<>();

q.offer(root);

int lvl = 0;

TreeMap<Integer, Integer> map = new TreeMap<>();

while(!q.isEmpty())

{

int size = q.size();

while(size-- > 0)

{

TreeNode cur = q.poll();

if(cur == null) continue;

map.put(lvl, cur.val);

q.offer(cur.left);

q.offer(cur.right);

}

lvl++;

}

List<Integer> list = new ArrayList<>();

for(int k : map.keySet()) list.add(map.get(k));

return list;

}

}