594. Longest Harmonious Subsequence

1. Question

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.

2. Examples

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

3. Constraints

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

4. References

来源：力扣（LeetCode） 链接：https://leetcode-cn.com/problems/longest-harmonious-subsequence 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

5. Solutions

class Solution {
  public int findLHS(int[] nums) {
    int ans = 0;
    HashMap<Integer, Integer> map = new HashMap<>();

    for (int i : nums) {
      map.put(i, map.getOrDefault(i, 0) + 1);
    }

    for (Integer key : map.keySet()) {
      if (map.containsKey(key + 1)) {
        ans = Math.max(ans, map.get(key) + map.get(key + 1));
      }
    }

    return ans;
  }
}