leetcode------Binary Tree Right Side View

标题：	Binary Tree Right Side View
通过率：	27.9%
难度：	中等

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].

 本题就是个按层次遍历的一种延伸，按层遍历时每次讲每一层的最后一个元素放入结果的list中即可，代码如下：

 1 /**

 2  * Definition for binary tree

 3  * public class TreeNode {

 4  *     int val;

 5  *     TreeNode left;

 6  *     TreeNode right;

 7  *     TreeNode(int x) { val = x; }

 8  * }

 9  */

10 public class Solution {

11     public ArrayList<Integer> rightSideView(TreeNode root) {

12         ArrayList<Integer> res=new ArrayList<Integer>();

13         LinkedList<TreeNode> queue=new LinkedList<TreeNode>();

14         int count=1,tmp=0;

15         if(root==null)return res;

16         queue.addLast(root);

17         while(!queue.isEmpty()){

18             tmp=0;

19             for(int i=1;i<=count;i++){

20                 TreeNode tmptree=queue.removeFirst();

21                 if(i==count)res.add(tmptree.val);

22                 if(tmptree.left!=null){

23                     queue.addLast(tmptree.left);

24                     tmp++;

25                 }

26                 if(tmptree.right!=null){

27                     queue.addLast(tmptree.right);

28                     tmp++;

29                 }

30                 

31             }

32             count=tmp;

33         }

34         return res;

35     }

36 }