LeetCode 760 · Binary Tree Right Side View.java

	// There is a little improvement from regular BFS,
	// This question needs to read the last one, and the queue does not support it.
	// But ArrayDeque itself does support it, so you only need to use the Deque interface, and you can play as you like.
	public class Solution {
	/**
	* @param root: the root of the given tree
	* @return: the values of the nodes you can see ordered from top to bottom
	*/
	public List<Integer> rightSideView(TreeNode root) {
	// write your code here
	if (root == null) {
	return new LinkedList<>();
	}
	return bfs(root);
	}
	private List<Integer> bfs(TreeNode root) {
	List<Integer> list = new LinkedList<>();
	Deque<TreeNode> queue = new ArrayDeque<>();
	queue.add(root);
	while (!queue.isEmpty()) {
	int size = queue.size();
	list.add(queue.peekLast().val);
	while (size-- > 0) {
	TreeNode node = queue.poll();
	if (node.left != null) {
	queue.add(node.left);
	}
	if (node.right != null) {
	queue.add(node.right);
	}
	}
	}
	return list;
	}
	}

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