```
class Solution(object):
def numberOfArithmeticSlices(self, A):
n = len(A)
if n < 3: return 0
dp = [None] * n
dp[0] = dp[1] = 0
curr, diff, l = A[0]-A[1], 0, 2
for i in range(1,n-1):
diff = A[i]-A[i+1]
if curr == diff:
l += 1
dp[i+1] = dp[i]+(l-3)+1 if l >= 3 else dp[i]
else:
dp[i+1] = dp[i]
curr, l = diff, 2
return dp[-1]
```