二叉树类高频算法题golang实现

Posted 2022-03-02 Kris_u

1、二叉树的先序遍历、中序遍历、后序遍历

先序遍历：根节点-->左子树--->右子树

type TreeNode struct
    Value int
    Left,Right *TreeNode


func (node *TreeNode) traverse()
	if node ==nil
		return
	
	fmt.Print(node.Value+" ")
	node.Left.traverse()
	node.Right.traverse()

中序遍历：左子树--->根节点---->右子树

func (node *TreeNode) traverse()
	if node ==nil
		return
	
	node.Left.traverse()
    fmt.Print(node.Value+" ")
	node.Right.traverse()

后序遍历：左子树--->右子树--->根节点

func (node *TreeNode) traverse()
	if node ==nil
		return
	
	node.Left.traverse()
	node.Right.traverse()
    fmt.Print(node.Value+" ")

2、二叉树的层次遍历

type TreeNode struct 
	Val   int
	Left  *TreeNode
	Right *TreeNode

func levelOrder(root *TreeNode) [][]int 
	if root == nil 
		return nil
	
	res := [][]int
	que := []*TreeNoderoot //队列
	for len(que) > 0 
		queSize := len(que) //当前层的节点数目
		current := []int //存储当前层的节点值
		for i := 0; i < queSize; i++ 
			out := que[0] //取出队列的第一个节点
			que = que[1:] //删除队列的第一个节点
			current = append(current, out.Val) 
			if out.Left != nil 
				que = append(que, out.Left)
			
			if out.Right != nil 
				que = append(que, out.Right)
			
		
		res = append(res, current) //将每层节点值的数组追加到二维数组res
	
	return res

3、二叉树的锯齿形层次遍历

func zigzagLevelOrder(root *TreeNode) (ans [][]int) 
	if root == nil 
		return nil
	
	res := [][]int
	que := []*TreeNoderoot //队列
	for l := 0; len(que) > 0; l++ 
		queSize := len(que) //当前层的节点数目
		current := []int  //存储当前层的节点值
		for i := 0; i < queSize; i++ 
			out := que[0] //取出队列的第一个节点
			que = que[1:] //删除队列的第一个节点

			if out.Left != nil 
				que = append(que, out.Left)
			
			if out.Right != nil 
				que = append(que, out.Right)
			
			current = append(current, out.Val)
		
		if l%2 != 0  //根据l%2是否为零，决定先从左往右，还是先从右往左
			for j := 0; j < len(current)/2; j++ 
				index := len(current) - j - 1
				if j != index 
					current[j], current[index] = current[index], current[j]
				
			
		
		res = append(res, current) //将每层节点值的数组追加到二维数组res
	
	return res

func main() 
	//创建一棵树、
	root := new(TreeNode)
	root.Val = 9
	left1 := new(TreeNode)
	left1.Val = 6
	right1 := new(TreeNode)
	right1.Val = 8
	left2 := new(TreeNode)
	left2.Val = 3
	right2 := new(TreeNode)
	right2.Val = 5
	root.Left = left1
	root.Right = right1
	left1.Left = left2
	right1.Right = right2

	levelOrder(root)
	zigzagLevelOrder(root)

编译输出：
levelOrder:res  [[9] [6 8] [3 5]]
zigzagLevelOrder:res  [[9] [8 6] [3 5]]  //  l%2 != 0 
zigzagLevelOrder:res  [[9] [6 8] [5 3]]  //  l%2 == 0