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103.java
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/**
* 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<List<Integer>> zigzagLevelOrder(TreeNode root) {
if (root == null) {
return new LinkedList<>();
}
List<List<Integer>> ans = new ArrayList<>();
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);
int k = 0;
while (!queue.isEmpty()) {
List<Integer> vals = new ArrayList<>();
int length = queue.size();
for (int i = 0; i < length; i++) {
TreeNode node = queue.poll();
vals.add(node.val);
if (node.left != null) {
queue.add(node.left);
}
if (node.right != null) {
queue.add(node.right);
}
}
if (k % 2 != 0) {
// System.out.println(k);
Collections.reverse(vals);
}
k++;
ans.add(vals);
}
return ans;
}
}