Find All Strict Interior Peak Indices

# Find All Strict Interior Peak Indices You are given a 0-indexed integer array `mountain`. An interior index `i` is a peak when its value is strictly greater than both neighboring values: `mountain[i] > mountain[i - 1]` and `mountain[i] > mountain[i + 1]`. The first and last indices are never peaks. Return the indices of all peaks in any order. ### Examples **Example 1** ```text Input: mountain = [5,9,2,6,1,7] Output: [1,3] ``` Value `9` at index `1` is greater than `5` and `2`; value `6` at index `3` is greater than `2` and `1`. The final value `7` is not eligible because it is an endpoint. Returning `[3,1]` would also be valid. **Example 2** ```text Input: mountain = [7,4,4,2] Output: [] ``` The interior values at indices `1` and `2` each equal a neighbor, so neither is strictly greater than both neighbors. Endpoints are excluded. ### Constraints - `3 <= mountain.length <= 100`. - `1 <= mountain[i] <= 100`. ### Clarifying Questions - Do equal neighboring values form a peak? No; both comparisons must be strict. - Can the first or last position qualify? No, regardless of its value. - Does the name `mountain` guarantee a single peak or a rise followed by a fall? No such shape promise is given; find every index satisfying the local definition. - Must peak indices be sorted? No; any order is permitted. - What should be returned when no peak exists? An empty array. ### C++ Interface ```cpp class Solution { public: vector<int> findPeaks(vector<int>& mountain) { } }; ``` ### Reasoning Checkpoints - Apply the strict two-neighbor definition without assuming a global array shape. - Exclude endpoints and include every qualifying interior index exactly once. - Preserve the any-order result contract and distinguish output storage from working space. ```hint Check each eligible position Inspect only indices with both a left and a right neighbor. What two comparisons exactly match the peak definition? ```