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BinaryTreeZigZag.java
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BinaryTreeZigZag.java
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import java.util.*;
/**
* 103. Binary Tree Zigzag Level Order Traversal
* BFS
* @author LBW
*/
public class BinaryTreeZigZag {
public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
List<TreeNode> queue = new LinkedList<>();
if (root != null)
queue.add(root);
boolean inOrder = false;
List<List<Integer>> res = new ArrayList<>();
while (!queue.isEmpty()) {
int size = queue.size();
// add list to res
List<Integer> list = new ArrayList<>();
if (inOrder) {
for (int i = size - 1; i >= 0; i--) {
list.add(queue.get(i).val);
}
}
else {
for (int i = 0; i < size; i++) {
list.add(queue.get(i).val);
}
}
res.add(list);
// add next level
for (int i = 0; i < size; i++) {
TreeNode cur = queue.get(0);
queue.remove(0);
if (cur.left != null)
queue.add(cur.left);
if (cur.right != null)
queue.add(cur.right);
}
//reverse Order
inOrder = !inOrder;
}
return res;
}
}