A harmonic subsequence consists of only two numbers x and x+1. We can count the frequency of each number using a hash map and then find the maximum count(x) + count(x+1).

1. Count frequencies of all numbers in nums using Counter.
2. max_len = 0.
3. For each x in the counter:
   • If x + 1 is also in the counter:
     • max_len = max(max_len, count[x] + count[x+1]).
4. Return max_len.

• Time Complexity: O(N).
• Space Complexity: O(N).

from collections import Counter

def find_lhs(nums):
    counts = Counter(nums)
    max_len = 0
    for x in counts:
        if x + 1 in counts:
            max_len = max(max_len, counts[x] + counts[x + 1])
    return max_len