code二叉树的右视图

原题链接:
https://leetcode.cn/problems/WNC0Lk/

/**
 * 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;
 *     }
 * }
 */
// 层序遍历 返回每层最右边的一个节点
class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        ArrayList<Integer> ans = new ArrayList<>();
        if(root == null){
            return ans;
        }

        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);

        while(!q.isEmpty()){
            int s = q.size();
            for(int i = 0 ; i < s ; i++){
                var node = q.poll();
                if(i == s - 1){
                    ans.add(node.val);
                }

                if(node.left != null){
                    q.offer(node.left);
                }

                if(node.right != null){
                    q.offer(node.right);
                }
            }
        }

        return ans;
    }
}