human
Solve in Python:
Given an unsorted array return whether an increasing subsequence of length 3 exists or not in the array.

Formally the function should:
Return true if there exists i, j, k  
such that arr[i] < arr[j] < arr[k] given 0 ≤ i < j < k ≤ n-1 
else return false.


Your algorithm should run in O(n) time complexity and O(1) space complexity.

Examples:
Given [1, 2, 3, 4, 5],
return true.

Given [5, 4, 3, 2, 1],
return false.

Credits:Special thanks to @DjangoUnchained for adding this problem and creating all test cases.
 Write me a the Python program you requested?
assistant
#Here is the Python program you requested.

class Solution:
     def increasingTriplet(self, nums):
         """
         :type nums: List[int]
         :rtype: bool
         """
         if nums == [] :
             return(False)
         min = nums[0]
         sec_min = (2**31 -1 )
         
         for i in nums :
             if i <= min :
                 min = i
             else :
                 if i <= sec_min :
                     sec_min = i
                 else :
                     return(True)
         return(False)