Stable Subarrays With Equal Boundary and Interior Sum

Description

You are given an integer array capacity.

A subarray capacity[l..r] is considered stable if:

- Its length is at least 3.

- The first and last elements are each equal to the sum of all elements strictly between them (i.e., capacity[l] = capacity[r] = capacity[l + 1] + capacity[l + 2] + ... + capacity[r - 1]).

Return an integer denoting the number of stable subarrays.