Find the Longest Strict Rise Followed by a Strict Fall

### Problem A mountain subarray has at least three consecutive entries, rises strictly to one interior peak, then falls strictly. Return the length of the longest such subarray, or zero when none exists. Flat steps are excluded. ```cpp class Solution { public: int longestMountain(vector<int>& arr); }; ``` ### Examples **Example 1:** ```text arr = [1,3,5,4,2] Output: 5 Explanation: The whole array rises to5 then falls. ``` **Example 2:** ```text arr = [1,2,2,1] Output: 0 Explanation: The plateau prevents a strict peak. ``` ### Constraints - Array length lies in [1,10000]. - Entries are integers from 0 through 10000. ### Contract considerations Require both strict sides and contiguous entries. ```hint Read the boundary condition When does a new rising edge mean the old mountain has ended? ``` ### Boundary reminders Require both strict sides and contiguous entries. ### Optional extensions - Can the scan use only one pass? - Can it retain only constant extra storage?