find all the longest subarrays which is arithmetic, sum up all the sub slices.

For a arithmetic subarray of length n, there are (n-1)(n-2)/2 arithmetic slices that can be constructed from it.

```
public int numberOfArithmeticSlices(int[] A) {
if(A==null||A.length<3) return 0;
int left=0, right=2;
int count=0;
while(right<A.length){
while(right<A.length&&A[right]-A[right-1]==A[right-1]-A[right-2]) right++;
if(right-left>=3) count+=(right-left-1)*(right-left-2)/2;
left=right++-1;
}
return count;
}
```