Create count-of-interesting-subarrays.py

Python/count-of-interesting-subarrays.py

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+# Time:  O(n)
+# Space: O(m)
+
+import collections
+
+
+# freq table, prefix sum
+class Solution(object):
+    def countInterestingSubarrays(self, nums, modulo, k):
+        """
+        :type nums: List[int]
+        :type modulo: int
+        :type k: int
+        :rtype: int
+        """
+        cnt = collections.Counter([0])
+        result = prefix = 0
+        for x in nums:
+            if x%modulo == k:
+                prefix = (prefix+1)%modulo
+            result += cnt[(prefix-k)%modulo]
+            cnt[prefix] += 1
+        return result