verify-preorder-sequence-in-binary-search-tree.md

Given an array of numbers, verify whether it is the correct preorder traversal sequence of a binary search tree.

You may assume each number in the sequence is unique.

Consider the following binary search tree: 

     5
    / \
   2   6
  / \
 1   3

Example 1:

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

Example 2:

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

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