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?