Golang二叉树重建，先序中序->后序，先序后序->中序，中序后序->先序

根据先序中序->后序，先序后序->中序，中序后序->先序，构建二叉树的方法，注意根据先序后序构建中序并不是唯一的，下面的代码以字符串模拟,若要还原树结构，将关键部分换成node即可

package main

import "fmt"

func prein2post(preorder string, inorder string) string {
	if len(preorder) == 0 {
		return ""
	}
	idx := 0
	for inorder[idx] != preorder[0] {
		idx++
	}
	ll := prein2post(preorder[1:1+idx], inorder[:idx])
	rr := prein2post(preorder[1+idx:], inorder[idx+1:])
	return ll + rr + string(preorder[0])
}

func prepost2in(pre string, post string) string {
	if len(pre) == 1 {
		return pre
	}
	idx := 0
	for post[idx] != pre[1] {
		idx++
	}
	ll := prepost2in(pre[1:1+idx+1], post[0:idx+1])
	rr := prepost2in(pre[1+idx+1:], post[1+idx:len(post)-1])
	return ll + string(pre[0]) + rr
}

func inpost2pre(in string, post string) string {
	if len(post) == 0 {
		return ""
	}
	cur := post[len(post)-1]
	idx := 0
	for in[idx] != cur {
		idx++
	}
	ll := inpost2pre(in[:idx], post[:idx])
	rr := inpost2pre(in[idx+1:], post[idx:len(post)-1])
	return string(cur) + ll + rr

}

func main() {
	pre := "ABCDE"  //   	A
	in := "CBDAE"   //	   B E
	post := "CDBEA" //	  C D
	fmt.Println(prein2post(pre, in) == post)
	fmt.Println(prepost2in(pre, post) == in)
	fmt.Println(inpost2pre(in, post) == pre)
}