二叉树的锯齿形层次遍历-二叉树

leetcode-103 二叉树的锯齿形层次遍历

这题与102题无异，只需对于保存结果的偶数行进行一次反转。可用（Collections.reverse（））

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
        List<List<Integer>> res = new ArrayList<>();
        if (root == null) return res;

        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);
        while(! q.isEmpty()){
            int size = q.size();
            List<Integer> list = new ArrayList<>();
            for (int i = 0; i < size; i++){
                TreeNode node = q.poll();
                list.add(node.val);
                if (node.left != null){
                    q.offer(node.left);
                }
                if (node.right != null){
                    q.offer(node.right);
                }
            }
            res.add(list);
        } 
        // 翻转偶数行
        for (int i = 0; i < res.size(); i++){
            if (i % 2 == 1){
                Collections.reverse(res.get(i));
            }
        }
        return res;
    }
}

本文地址：https://blog.csdn.net/liu_tian_wei/article/details/109636675