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Commit 46734b7

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commit solution 103
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‎solution/100-199/0103.binary-tree-zigzag-level-order-traversal/README.md

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# [100. xxx](https://leetcode-cn.com/problems/recover-binary-search-tree)
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# [103. 二叉树的锯齿形层次遍历](https://leetcode-cn.com/problems/binary-tree-zigzag-level-order-traversal/description/)
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### 题目描述
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<p>给定一个二叉树,返回其节点值的锯齿形层次遍历。(即先从左往右,再从右往左进行下一层遍历,以此类推,层与层之间交替进行)。</p>
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<p>例如:<br>
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给定二叉树&nbsp;<code>[3,9,20,null,null,15,7]</code>,</p>
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<pre> 3
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/ \
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9 20
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/ \
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15 7
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</pre>
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<p>返回锯齿形层次遍历如下:</p>
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<pre>[
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[3],
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[20,9],
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[15,7]
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]
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</pre>
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### 解题思路
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1. BFS
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### 具体解法
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<!-- tabs:start -->
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#### **Golang**
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```go
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type TreeNode struct {
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Val int
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Left *TreeNode
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Right *TreeNode
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}
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func zigzagLevelOrder(root *TreeNode) [][]int {
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res := [][]int{}
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if root == nil {
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return res
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}
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queue := []*TreeNode{root}
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for level := 0; len(queue) > 0; level++ {
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l := len(queue)
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list := []int{}
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for i := 0; i < l; i++ {
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node := queue[i]
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if level%2 == 0 {
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list = append(list, node.Val)
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} else {
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list = append([]int{node.Val}, list...)
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}
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if node.Left != nil {
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queue = append(queue, node.Left)
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}
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if node.Right != nil {
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queue = append(queue, node.Right)
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}
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}
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queue = queue[l:]
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res = append(res, list)
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}
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return res
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}
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```
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<!-- tabs:end -->
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package leetcode
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/*
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* @lc app=leetcode.cn id=103 lang=golang
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*
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* [103] 二叉树的锯齿形层次遍历
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* type TreeNode struct {
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* Val int
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* Left *TreeNode
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* Right *TreeNode
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* }
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*/
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type TreeNode struct {
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Val int
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Left *TreeNode
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Right *TreeNode
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}
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func zigzagLevelOrder(root *TreeNode) [][]int {
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res := [][]int{}
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if root == nil {
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return res
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}
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queue := []*TreeNode{root}
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for level := 0; len(queue) > 0; level++ {
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l := len(queue)
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list := []int{}
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for i := 0; i < l; i++ {
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node := queue[i]
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if level%2 == 0 {
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list = append(list, node.Val)
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} else {
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list = append([]int{node.Val}, list...)
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}
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if node.Left != nil {
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queue = append(queue, node.Left)
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}
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if node.Right != nil {
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queue = append(queue, node.Right)
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}
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}
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queue = queue[l:]
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res = append(res, list)
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}
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return res
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}
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// @lc code=end

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