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：

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ArrayList<Integer> rightSideView(TreeNode root) {
        ArrayList<Integer> res=new ArrayList<Integer>();
        LinkedList<TreeNode> queue=new LinkedList<TreeNode>();
        int count=1,tmp=0;
        if(root==null)return res;
        queue.addLast(root);
        while(!queue.isEmpty()){
            tmp=0;
            for(int i=1;i<=count;i++){
                TreeNode tmptree=queue.removeFirst();
                if(i==count)res.add(tmptree.val);
                if(tmptree.left!=null){
                    queue.addLast(tmptree.left);
                    tmp++;
                }
                if(tmptree.right!=null){
                    queue.addLast(tmptree.right);
                    tmp++;
                }
                
            }
            count=tmp;
        }
        return res;
    }
}