package main

type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

func main() {

}
func buildTree(preorder []int, inorder []int) *TreeNode {

	var builder func(p []int, in []int) *TreeNode
	builder = func(p []int, in []int) *TreeNode {
		if len(in) == 0 || len(p) == 0 {
			return nil
		}
		rootnum := p[0]
		value := -1
		for i := 0; i < len(in); i++ {
			if in[i] == rootnum {
				value = i

			}
		}
		var left []int
		var right []int
		if value != -1 {
			left = in[:value]
			right = in[value+1:]
		} else {
			return nil
		}
		tmp := &TreeNode{
			Val:   rootnum,
			Left:  builder(p[1:1+len(left)], left),
			Right: builder(p[1+len(left):], right),
		}
		return tmp
	}

	res := builder(preorder, inorder)

	return res
}