Add solution for Binary Subarrays With Sum

week9/leetcode/binary-subarrays-with-sum.py

@@ -0,0 +1,15 @@
+class Solution:
+    def numSubarraysWithSum(self, nums: List[int], goal: int) -> int:
+        def atmost(nums,goal):
+            left=0
+            count=0
+            cur=0
+            for right in range(len(nums)):
+                cur+=nums[right]
+                while cur>goal and left<=right:
+                    cur-=nums[left]
+                    left+=1
+                count+=right-left+1
+            return count
+        return atmost(nums,goal)-atmost(nums,goal-1)
+