Array Increasing Triplet Sequence LeetCode

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 
• Return false otherwise.

Example 1:

• Input: [1,2,3,4,5]
• Output: true

Example 2:

• Input: [5,4,3,2,1]
• Output: false

NOTE: 

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

This is a problem from LeetCode and is also discussed in GeeksForGeeks A collection of hundreds of interview questions and solutions are available in our blog at Interview Question Solutions

Solution: