Maximum Value of an Ordered Triplet I — Python

# Time:  O(n)
# Space: O(1)

# array
class Solution(object):
    def maximumTripletValue(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        NEG_INF = float("-inf")
        result = 0
        mx_diff = mx = NEG_INF
        for x in nums:
            if mx_diff != NEG_INF:
                result = max(result, mx_diff*x)
            if mx != NEG_INF:
                mx_diff = max(mx_diff, mx-x)
            mx = max(mx, x)
        return result