523. continuous subarray sum

Given an integer array nums and an integer k, return true if nums has a good subarray or false otherwise.

A good subarray is a subarray where:

• its length is at least two, and
• the sum of the elements of the subarray is a multiple of k.

Note that:

• A subarray is a contiguous part of the array.
• An integer x is a multiple of k if there exists an integer n such that x = n * k. 0 is always a multiple of k.

solution

def checkSubarraySum(self, nums: List[int], k: int) -> bool:
	"""
	k = 6
	[0, 23, 25, 29, 35, 42]
	we can then make the prefix sums mod k
	[0, 5, 1, 5, 5, 0]
	  
	we can construct prefix, hashmap as we iterate right,
	look back to see if mod exists to the left
 
	if it does, the difference between two numbers of same mod k
	will be a multiple of k
	  
	length at least 2, so a single value with mod 0 won't work
	"""
  
	seen_mods = set()
	prefix_sums = [0]
	for num in nums:
		prefix_sums.append(prefix_sums[-1] + num)
		mod = prefix_sums[-1] % k
	  
		if mod in seen_mods:
			return True
		seen_mods.add(prefix_sums[-2] % k)
	return False