Create binary-subarrays-with-sum.py

Author: kamyu104

Python/binary-subarrays-with-sum.py

@@ -0,0 +1,26 @@
+# Time:  O(n)
+# Space: O(1)
+
+# Two pointers solution
+class Solution(object):
+    def numSubarraysWithSum(self, A, S):
+        """
+        :type A: List[int]
+        :type S: int
+        :rtype: int
+        """
+        result = 0
+        left, right, sum_left, sum_right = 0, 0, 0, 0
+        for i, a in enumerate(A):
+            sum_left += a
+            while left < i and sum_left > S:
+                sum_left -= A[left]
+                left += 1
+            sum_right += a
+            while right < i and \
+                  (sum_right > S or (sum_right == S and not A[right])):
+                sum_right -= A[right]
+                right += 1
+            if sum_left == S:
+                result += right-left+1
+        return result