Count-distinct problem is a problem of finding the number of distinct elements in a data set or data stream, within which you might possibly see some repeated elements. For example,
[1, 3, 2, 1, 5, 2, 4] has 5 distinct elements
[1, 2, 3, 4, 5].
HyperLogLog is an algorithm that can solve Count Distinct problem. It can provide estimated count on a very large data stream.
MurmurHash is in the family of general purpose hashing algorithms. In particular, it's only suitable for non-cryptographic usage.
Given dict D, array nums, * any j: D.get(nums[j]) = j, 0 <= j < lens(nums). * exist i: D.get(target - nums[j]) = i, iff target - nums[j] in D.
Hint: Reducing variables in the problem is the key to a simpler solution.