[LeetCode]Binary Tree Right Side View

原题链接：https://leetcode.com/problems/binary-tree-right-side-view/

题意描述：

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].

题解：

这道题非常有趣，是找二叉树从右侧看的时候能看到的数，其实思路也是很简单，即返回每一层的最右边的一个数就好了，在二叉树的层序遍历的代码上稍作修改即可。对二叉树的层序遍历不太清楚的朋友，可看我之前的博客《二叉树完全总结》。具体没什么好说的，直接上代码：

 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 List<Integer> rightSideView(TreeNode root) {

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

13         if(root==null)

14             return res;

15         Queue<TreeNode> Q = new LinkedList<TreeNode>(); 

16         Q.offer(root);

17         int curLevel = 1;

18         res.add(root.val);

19         while(!Q.isEmpty()){

20             int levelSize = Q.size();

21             int count = 0;

22             TreeNode last = null;

23             while(count<levelSize){

24                 TreeNode p = Q.poll();

25                 if(p.left!=null){

26                     last = p.left;

27                     Q.offer(p.left);

28                 }

29                 if(p.right!=null){

30                     last = p.right;

31                     Q.offer(p.right);

32                 }

33                 count++;

34             }

35             if(last!=null)

36                 res.add(last.val);

37             

38         }

39         return res;

40     }

41 }