Binary Tree Right Side View *

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

For example:
Given the following binary tree,

   1            <---
 /   
2     3         <---
      
  5     4       <---

You should return [1, 3, 4].

层序遍历二叉树，依次输出每层最右节点即可，代码如下：

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        List<Integer> re_list = new ArrayList<Integer>();
        List<TreeNode> level_list = new ArrayList<TreeNode>();//层序遍历时存储当前层节点的list
        List<TreeNode> tmp_list = new ArrayList<TreeNode>();//用来存储下一层节点的list
        if(root==null) return re_list;
        level_list.add(root);
        re_list.add(root.val);
        int flag = 1;
        while(flag==1) {
            flag = 0;
            tmp_list.clear();
            for(TreeNode node:level_list) {
                if(node.left!=null) {
                    flag = 1;//说明下层还存在节点
                    tmp_list.add(node.left);
                }
                if(node.right!=null) {
                    flag = 1;//说明下层还存在节点
                    tmp_list.add(node.right);
                }
            }
            int size = tmp_list.size();
            if(tmp_list.size()!=0) {
                re_list.add(tmp_list.get(size-1).val);//记录当前层最右边节点
                level_list.clear();
                level_list.addAll(tmp_list);//迭代
            }
        }
        return re_list;
    }
}