```
class Solution(object):
def numberOfArithmeticSlices(self, A):
"""
:type A: List[int]
:rtype: int
"""
if len(A) < 3:
return 0
result = 0
start = 0
diff = A[1] - A[0]
j = 2
while j < len(A):
if A[j]-A[j-1]!=diff:
l = j - start
result = result + l*(l-2) - (l-2)*(l+1)/2
diff = A[j] - A[j-1]
start = j-1
j = j + 1
l = j - start
result = result + l*(l-2) - (l-2)*(l+1)/2
return result
```