199. Binary Tree Right Side View (二叉树右视图)
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.
Example:
Input: [1,2,3,null,5,null,4]
Output: [1, 3, 4]
Explanation:
1 <---
/ \
2 3 <---
\ \
5 4 <---
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public List<Integer> rightSideView(TreeNode root) {
List<Integer> list = new ArrayList<>();
Queue<TreeNode> queue = new LinkedList<>();
if(root == null){
return list;
}
queue.add(root);
while(!queue.isEmpty()){
int size = queue.size();
for(int i=0; i<size; i++){
TreeNode node = queue.poll();
if(node.left!=null){
queue.add(node.left);
}
if(node.right!=null){
queue.add(node.right);
}
if(i == size-1){
list.add(node.val);
}
}
}
return list;
}
}