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// @Title: 二叉树的锯齿形层序遍历 (Binary Tree Zigzag Level Order Traversal)
// @Author: 15816537946@163.com
// @Date: 2020-12-22 23:55:08
// @Runtime: 0 ms
// @Memory: 2.9 MB
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func zigzagLevelOrder(root *TreeNode) [][]int {
	res := [][]int{}

	var dfs func(*TreeNode, int)
	dfs = func(node *TreeNode, level int) {
		if node == nil {
			return
		}

		if level >= len(res) {
			res = append(res, []int{})
		}

		if level%2 == 0 {
			res[level] = append(res[level], node.Val)
		} else {
			// 翻转列表
			tmp := make([]int, len(res[level])+1)
			tmp[0] = node.Val
			copy(tmp[1:], res[level])
			res[level] = tmp
		}

		dfs(node.Left, level+1)
		dfs(node.Right, level+1)
	}

	dfs(root, 0)

	return res
}