Problem:
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 [5,1],
return false.

Answer:

=num) return 0;
    for(;inums[i]&&num=3) return true;
    else return false;
};