Unstable Subarray

You are given an array $A$ of size $N$. We define the function $f(l, r) = \sum_{i=l}^{r-1}(A_i-A_{i+1})$, where $1\le l \le r \le N$. Note that $f(i, i)$ is defined as $0$. A subarray $A[l, r]$ is considered *unstable* if $f(l,r) \neq (A_r-A_l)$. Count the number of *unstable* subarrays in the array. Note that the subarray $A[l, r]$ consists of $A_l, A_{(l+1)}, \ldots, A_{(r-1)}, A_r$. ##