package 树的遍历.q103_二叉树的锯齿形层序遍历;
public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) {
val = x;
}
}
package 树的遍历.q103_二叉树的锯齿形层序遍历;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
/**
* 和层序遍历相同,额外加一个标记控制插入队列的位置
*/
public class Solution {
public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
List<List<Integer>> ans = new ArrayList<>();
if (root == null) {
return ans;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);
boolean flag = true;
while (!queue.isEmpty()) {
List<Integer> list = new ArrayList<>();
int size = queue.size();
while (size > 0) {
TreeNode tn = queue.poll();
if (flag) {
list.add(tn.val);
} else {
list.add(0, tn.val);
}
if (tn.left != null) {
queue.add(tn.left);
}
if (tn.right != null) {
queue.add(tn.right);
}
size--;
}
flag = !flag;
ans.add(list);
}
return ans;
}
}