剑指 Offer 32 - III. 从上到下打印二叉树 III
LinkedList
list. addLast
list.addFirst
list.add--->从后面添加元素
class Solution {
public List<List<Integer>> levelOrder(TreeNode root) {
List<List<Integer>> res=new ArrayList<>();
if(root==null) return res;
Queue<TreeNode> q=new LinkedList<>();
q.add(root);
while(!q.isEmpty()){
int size=q.size();
LinkedList<Integer> list=new LinkedList<>();
for(int i=0;i<size;i++){
TreeNode node=q.poll();
if(res.size()%2==0) list.addLast(node.val);
else list.addFirst(node.val);
if(node.left!=null) q.add(node.left);
if(node.right!=null) q.add(node.right);
}
res.add(list);
}
return res;
}
}