思路

层序遍历 从左向右遍历每一层取最后一个数，代码如下：

public List<Integer> rightSideView(TreeNode root) {if (root==null){return new ArrayList<>();}Queue<TreeNode> queue = new LinkedList<>();List<Integer> list = new ArrayList<>();TreeNode cur=root;queue.add(cur);while (!queue.isEmpty()){int size = queue.size();for (int i = 0; i < size; i++) {cur = queue.poll();if (i==size-1){list.add(cur.val);}if (cur.left!=null){queue.add(cur.left);}if (cur.right!=null){queue.add(cur.right);}}}return list;}