<p>We define a harmonious array as an array where the difference between its maximum value and its minimum value is <b>exactly</b> <code>1</code>.</p> <p>Given an integer array <code>nums</code>, return <em>the length of its longest harmonious subsequence among all its possible subsequences</em>.</p> <p>A <strong>subsequence</strong> 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.</p> <p> </p> <p><strong>Example 1:</strong></p> <pre> <strong>Input:</strong> nums = [1,3,2,2,5,2,3,7] <strong>Output:</strong> 5 <strong>Explanation:</strong> The longest harmonious subsequence is [3,2,2,2,3]. </pre> <p><strong>Example 2:</strong></p> <pre> <strong>Input:</strong> nums = [1,2,3,4] <strong>Output:</strong> 2 </pre> <p><strong>Example 3:</strong></p> <pre> <strong>Input:</strong> nums = [1,1,1,1] <strong>Output:</strong> 0 </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= nums.length <= 2 * 10<sup>4</sup></code></li> <li><code>-10<sup>9</sup> <= nums[i] <= 10<sup>9</sup></code></li> </ul>