523. Continuous Subarray Sum

class Solution:
    def checkSubarraySum(self, nums, k):
        prefix_mod = 0
        mod_seen = defaultdict(int) 
        mod_seen[0] = -1
 
        for i, num in enumerate(nums):
            prefix_mod = (prefix_mod + num) % k
 
            if prefix_mod in mod_seen:
                if i - mod_seen[prefix_mod] > 1:
                    return True
            else:
                mod_seen[prefix_mod] = i
 
        return False