[Leetcode] binary tree 右视问题

[1] Populating Next Right Pointers in Each Node

[2] Populating Next Right Pointers in Each Node II

[3] Binary Tree Right Side View

 

一、参考我的另一篇博客

二、同一

三、使用层次遍历方式，但是要记录每一层的最后一个node

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
 import java.util.*;
public class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        List<Integer> res = new LinkedList<Integer>();
        if(root==null) return res;
        queue.offer(root);
        while(!queue.isEmpty()){
            int size = queue.size();
            TreeNode current = null;
            for(int i=0;i<size;i++){
                current = queue.poll();
                if(current.left!=null) queue.offer(current.left);
                if(current.right!=null) queue.offer(current.right);
            }
            res.add(current.val);
        }
        return res;
    }
}