leetocde_Binary Tree Right Side View

描述：

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].

思路：

按层序遍历的思路，每次只保存该层的最后一个元素即可。

代码：

public List<Integer> rightSideView(TreeNode root) {
        List<Integer>listReturn=new ArrayList<Integer>();
        if(root==null)
        	return listReturn;
        List<TreeNode>list=new ArrayList<TreeNode>();
        List<TreeNode>temp=new ArrayList<TreeNode>();
        list.add(root);
        TreeNode node=null;
        listReturn.add(root.val);
        while(list.size()!=0)
        {
        	for(int i=0;i<list.size();i++)
        	{
        		node=list.get(i);
        		if(node.left!=null)
        			temp.add(node.left);
        		if(node.right!=null)
        			temp.add(node.right);
        	}
        	if(temp.size()>0)
        		listReturn.add(temp.get(temp.size()-1).val);
        	list.clear();
            list=temp;
        	temp=new ArrayList<TreeNode>();
        }
	    return listReturn;
   }

结果：