Given an integer array capacity, return the total number of stable subarrays.

A subarray capacity[l...r] is considered stable if it satisfies the following conditions:

• The subarray has a length of at least $3$, which means $r - l \geq 2$.

• The boundary elements are equal, such that capacity[l] == capacity[r].

• The sum of the interior elements strictly between index l and index r is equal to capacity[l].

Constraints:

• $3 \leq$ capacity.length $\leq 10^5$

• $-10^9 \leq$ capacity[i] $\leq 10^9$

Now, let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.