package q105

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

func bld(preorder []int, inorder map[int]int, pL, pR, iL, iR int) *TreeNode {
	if pL == pR {
		return nil
	}

	val := preorder[pL]
	p := inorder[val] // position of val in "inorder"

	left := bld(preorder, inorder, pL+1, pL+1+p-iL, iL, p)
	right := bld(preorder, inorder, pL+1+p-iL, pR, p+1, iR)

	return &TreeNode{
		Val:   val,
		Left:  left,
		Right: right,
	}
}

func buildTree(preorder []int, inorder []int) *TreeNode {
	iIdx := make(map[int]int, len(inorder))
	for i := range inorder {
		iIdx[inorder[i]] = i
	}
	return bld(preorder, iIdx, 0, len(preorder), 0, len(preorder))
}

var _ = buildTree