Added Python solution for "Binary Subarrays With Sum"

Author: Kyrylo-Ktl

Python/Binary Subarrays With Sum.py

@@ -0,0 +1,21 @@
+from collections import defaultdict
+from itertools import accumulate
+from typing import List
+
+
+class Solution:
+    """
+    Time:   O(n)
+    Memory: O(n)
+    """
+
+    def numSubarraysWithSum(self, nums: List[int], target: int) -> int:
+        prefix_sums = defaultdict(int)
+        prefix_sums[0] = 1
+
+        sub_arrays = 0
+        for prefix in accumulate(nums):
+            sub_arrays += prefix_sums[prefix - target]
+            prefix_sums[prefix] += 1
+
+        return sub_arrays