Given an array of unique integers preorder, return true if it is the correct preorder traversal sequence of a binary search tree.

 

Example 1:

Input: preorder = [5,2,1,3,6]
Output: true

Example 2:

Input: preorder = [5,2,6,1,3]
Output: false

 

Constraints:

• 1 <= preorder.length <= 104
• 1 <= preorder[i] <= 104
• All the elements of preorder are unique.

 

Follow up: Could you do it using only constant space complexity?