代码随想录-06-二叉树-05.03.二叉树的右视图

二叉树的右视图

#模板题

题目描述

给定一个二叉树的 根节点 root，想象自己站在它的右侧，按照从顶部到底部的顺序，返回从右侧所能看到的节点值。

具体思路

• 层序遍历；
• 当每一层的队列大小剩余为1即size == 1时，收集结果；

具体代码

/**
 * 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 {

    private Queue<TreeNode> q = new ArrayDeque<>();
    List<Integer> res = new ArrayList<>();

    public List<Integer> rightSideView(TreeNode root) {
        if (root == null) {
            return res;
        }
        q.add(root);
        while (!q.isEmpty()) {
            int size = q.size();
            while (size > 0) {
                TreeNode cur = q.element();
                if (size == 1) {
                    res.add(cur.val);
                }
                q.remove();
                if (cur.left != null) {
                    q.add(cur.left);
                }
                if (cur.right != null) {
                    q.add(cur.right);
                }
                size--;

            }
        }
        return res;
    }
}