LeetCode199二叉树的右视图

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        if(root==null) return new ArrayList<Integer>();
        List<Integer> res=new ArrayList<>();
        Queue<TreeNode> q=new LinkedList<>();
        q.add(root);
        while(!q.isEmpty()){
            int size=q.size();//记录每层个数,把每层拿出来看
            while(size>0){
                TreeNode node=q.poll();
                if(node.left!=null)
                    q.add(node.left);
                if(node.right!=null)
                    q.add(node.right);
                if(size==1)
                    res.add(node.val);
                size--;
            }
        }
        return res;
        
    }
}