harmonicSequence

/**
 * We define a harmonious array as an array where the difference between its
 * maximum value and its minimum value is exactly `1`.
 *
 * Given an integer array `nums`, return the length of its longest harmonious
 * subsequence among all its possible subsequences.
 *
 * A subsequence of array is a sequence that can be derived from the array by
 * deleting some or no elements without changing the order of the remaining
 * elements.
 *
 * Example 1:
 * Input: nums = [1,3,2,2,5,2,3,7]
 * Output: 5
 * Explanation: The longest harmonious subsequence is [3,2,2,2,3].
 *
 * Example 2:
 * Input: [1,2,3,4]
 * Output: 2
 *
 * Example 3:
 * Input: [1,1,1,1]
 * Output: 0
 *
 * Example: 4
 * Input: [1,3,5,7,9,11,13,15,17]
 * Output: 0
 */