594 Longest Harmonious Subsequence

We define a harmonious array is an array where the difference between its maximum value and its minimum value is exactly1.

Now, given an integer array, you need to find the length of its longest harmonious subsequence among all its possible subsequences.

Example 1:

Input:
 [1,3,2,2,5,2,3,7]

Output:
 5

Explanation:
 The longest harmonious subsequence is [3,2,2,2,3].

Note:The length of the input array will not exceed 20,000.

The Idea: The first thing to understand is that if the maximum - minimum value of a subsequence is 1, then that subsequence can only contain values of the maximum and/or minimum since every other number above or below these would break the definition. So for every number in the array, we only need to keep track of a count of two things: a count of the number itself (which will serve as the minimum), and a count of the number greater than itself (which will serve as the maximum). Together, these will make up some subsequence in the input array.

Complexity: O(N) time and space

from collections import Counter


class Solution:
    def findLHS(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """

        hist = Counter(nums)
        maxx = 0
        for key, _ in hist.items():
            if key + 1 in hist:
                maxx = max(maxx, hist[key] + hist[key + 1])
        return maxx