Medium
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].
这道题居然一开始错用Stack来做了。来，跟我一起念：
BFS用Queue！BFS用Queue! BFS用Queue!
重要的事情说三遍！
接下来就跟Binary Level Order Traversal没什么两样了，只是每遍历完一层，要往res里添加该层最右边的节点值。
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public List<Integer> rightSideView(TreeNode root) {
List<Integer> res = new ArrayList<>();
if (root == null){
return res;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while (!queue.isEmpty()){
int size = queue.size();
List<Integer> level = new ArrayList<>();
for (int i = 0; i < size; i++){
TreeNode node = queue.poll();
level.add(node.val);
if (node.left != null){
queue.offer(node.left);
}
if (node.right != null){
queue.offer(node.right);
}
}
res.add(level.get(level.size() - 1));
}
return res;
}
}
