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 ¡Ü i < j < k ¡Ü 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.