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].
其实就是层序遍历 的每层的最后一个元素！！！！
1 class Solution { 2 3 public List<Integer> rightSideView(TreeNode root) { 4 List<Integer> res = new ArrayList<Integer>(); 5 Queue<TreeNode> queue = new LinkedList<TreeNode>(); 6 if(root==null) return res; 7 queue.offer(root); 8 int level_num = 1; 9 while (!queue.isEmpty()) { 10 level_num = queue.size(); 11 for(int i = 0; i < level_num; i++){ 12 TreeNode node = queue.poll(); 13 if(i==level_num-1) 14 res.add(node.val); 15 if(node.left != null) queue.offer(node.left); 16 if(node.right != null) queue.offer(node.right); 17 18 } 19 } 20 return res; 21 } 22 }