Given an integer array nums, return the length of the longest harmonious subsequence of nums.

A subsequence is formed by deleting zero or more elements from nums without changing the relative order of the remaining elements. A subsequence is called harmonious if the difference between its maximum value and minimum value is exactly $1$.

If no harmonious subsequence exists, return $0$.

Constraints:

• $1 \leq$ nums.length $\leq 2 \cdot 10^4$

• $-10^9 \leq$ nums[i] $\leq 10^9$

Input: nums = [4,4,5,5,5,6]-List[int]
Output: 5-int
Explanation: The best harmonious subsequence uses values 4 and 5 (difference 1), with counts 4 → 2 and 5 → 3, giving length 2 + 3 = 5. Including 6 would force the min/max difference to be 2, which is not allowed.

Input: nums = [10,10,10,10]-List[int]
Output: 0-int
Explanation: A harmonious subsequence must contain at least two distinct values whose difference is exactly 1. Here all values are the same, so no such subsequence exists.

Input: nums = [-2,-1,-1,-1,0,0,1]-List[int]
Output: 5-int
Explanation: Considering adjacent values, -2 and -1 give counts 1 + 3 = 4, -1 and 0 give 3 + 2 = 5 (the best), and 0 and 1 give 2 + 1 = 3, so the longest harmonious subsequence has length 5 using -1 and 0.

Input: nums = [1000000000,999999999,999999999,1000000000,-1000000000]-List[int]
Output: 4-int
Explanation: The only pair with difference 1 is 999999999 and 1000000000, with counts 999999999 → 2 and 1000000000 → 2, giving 2 + 2 = 4. The -1000000000 cannot be included because it would make the max-min difference far larger than 1.

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