Find the Longest Subsequence with Exact Value Spread One

### Problem A harmonious subsequence has maximum value minus minimum value exactly one. Return the greatest length of such a subsequence of nums, or zero if none exists. Selected elements retain their original order but need not be adjacent. ```cpp class Solution { public: int findLHS(vector<int>& nums); }; ``` ### Examples **Example 1:** ```text nums = [4,5,4,9,5,5] Output: 5 Explanation: Keep all occurrences of 4 and 5. ``` **Example 2:** ```text nums = [-2,-2,-2] Output: 0 Explanation: A spread of zero does not qualify. ``` ### Constraints - Input size: 1..20000 integers, with values in -1000000000..1000000000. ### Clarifying Questions Require both consecutive values and retain every eligible occurrence in their original order. ```hint Read the boundary condition Which integer values can occur when maximum minus minimum equals one? ``` ### Contract considerations Require both consecutive values and retain every eligible occurrence in their original order.