334.py

'''
	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.
'''

class Solution(object):
    def increasingTriplet(self, nums):
        """
        :type nums: List[int]
        :rtype: bool
        """
        
        first, second = float('inf'), float('inf')
        for val in nums:
        	if val <= first:
        		first = val
        	elif val <= second:
        		second = val
        	else:
        		return True

        return False