import java.util.*;
/*
层次遍历的变形
*/
class Solution {
public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
Queue<TreeNode> queue = new LinkedList<>();
if(root == null){
return res;
}
queue.add(root);
int l2r = 1;
while(!queue.isEmpty()){
List<Integer> cur = new ArrayList<>();
int size = queue.size();
for(int i = 0; i < size; i++){
TreeNode node = queue.poll();
cur.add(node.val);
if(node.left != null){
queue.add(node.left);
}
if(node.right != null){
queue.add(node.right);
}
}
if(l2r == -1){
Collections.reverse(cur);
}
res.add(cur);
l2r = -l2r;
}
return res;
}
}