Question

594. Longest Harmonious Subsequence

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Description

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: nums = [1,2,3,4]

Output: 2

Example 3:

Input: nums = [1,1,1,1]

Output: 0

 

Constraints:

• 1 <= nums.length <= 2 * 104
• -109 <= nums[i] <= 109

Solutions

Solution 1

class Solution:
  def findLHS(self, nums: List[int]) -> int:
    ans = 0
    counter = Counter(nums)
    for num in nums:
      if num + 1 in counter:
        ans = max(ans, counter[num] + counter[num + 1])
    return ans

class Solution {
  public int findLHS(int[] nums) {
    Map<Integer, Integer> counter = new HashMap<>();
    for (int num : nums) {
      counter.put(num, counter.getOrDefault(num, 0) + 1);
    }
    int ans = 0;
    for (int num : nums) {
      if (counter.containsKey(num + 1)) {
        ans = Math.max(ans, counter.get(num) + counter.get(num + 1));
      }
    }
    return ans;
  }
}

class Solution {
public:
  int findLHS(vector<int>& nums) {
    unordered_map<int, int> counter;
    for (int num : nums) {
      ++counter[num];
    }
    int ans = 0;
    for (int num : nums) {
      if (counter.count(num + 1)) {
        ans = max(ans, counter[num] + counter[num + 1]);
      }
    }
    return ans;
  }
};

func findLHS(nums []int) int {
  counter := make(map[int]int)
  for _, num := range nums {
    counter[num]++
  }
  ans := 0
  for _, num := range nums {
    if counter[num+1] > 0 {
      ans = max(ans, counter[num]+counter[num+1])
    }
  }
  return ans
}

Solution 2

class Solution:
  def findLHS(self, nums: List[int]) -> int:
    counter = Counter(nums)
    return max(
      [counter[num] + counter[num + 1] for num in nums if num + 1 in counter],
      default=0,
    )