199.二叉树的右视图.java

/*
 * @lc app=leetcode.cn id=199 lang=java
 *
 * [199] 二叉树的右视图
 */

// @lc code=start
/**
 * 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) {

        List<Integer> res=new ArrayList<>();
        if(root==null){
            return res;
        }
        Queue<TreeNode> queue=new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()){
            int size=queue.size();
            for(int i=0;i<size;i++){
                TreeNode temp=queue.poll();

                if(i==size-1){
                    res.add(temp.val);
                }


                if(temp.left!=null){
                    queue.offer(temp.left);
                }

                if(temp.right!=null){
                    queue.offer(temp.right);
                }
            }
            
        }

        return res;
    }
}
// @lc code=end