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.

findLHS.js

/**
 * @param {number[]} nums
 * @return {number}
 */
var findLHS = function(nums) {
    const freqMap = new Map(); // To store frequency of each number
    let maxLength = 0;

    // Step 1: Count the frequency of each number
    for (const num of nums) {
        freqMap.set(num, (freqMap.get(num) || 0) + 1);
    }

    // Step 2: Check if a consecutive number exists for each key
    for (const [key, count] of freqMap.entries()) {
        if (freqMap.has(key + 1)) {
            const nextCount = freqMap.get(key + 1);
            // Calculate the length of the potential harmonious subsequence
            maxLength = Math.max(maxLength, count + nextCount);
        }
    }

    return maxLength;
};