Problem Statement

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. [URL]

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

Example 1: 

Input: [1,2,3,4,5]
Output: true

Example 2: 

Input: [5,4,3,2,1]
Output: false

Approach 1 

#collapse-hide
from typing import List

class Solution:
    def increasingTriplet(self, nums: List[int]) -> bool:
        flagCount = 0
        for i in range(len(nums)):
            if 

sol = Solution()

sol.increasingTriplet([7,8,9,11,12])

1

Worst case performance in Time: $O(nlogn)$

Worst case performance in Space: $O(1)$