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ZigagLevelOrderTraversal.java
55 lines (46 loc) · 1.38 KB
/
ZigagLevelOrderTraversal.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;
* }
* }
*/
// https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/
class Solution {
public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
if (root == null) {
return res;
}
Deque<TreeNode> queue = new ArrayDeque<>();
int flag = 1;
queue.add(root);
while (!queue.isEmpty()) {
List<TreeNode> children = new ArrayList<>();
List<Integer> list = new ArrayList<>();
while (!queue.isEmpty()) {
TreeNode node = queue.removeFirst();
list.add(node.val);
if (node.left != null)
children.add(node.left);
if (node.right != null)
children.add(node.right);
}
queue.addAll(children);
if (flag == -1) {
Collections.reverse(list);
}
res.add(list);
flag = -flag;
}
return res;
}
}