594. Longest Harmonious Subsequence

Description

We define a harmonious array is an array where the difference between its maximum value and its minimum value is exactly 1.

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.

Solution

HashMap

此题目乍一看还有点迷惑性，仔细想来是求susequence，所以顺序也不重要了，直接用HashMap就轻松解决啦。

class Solution {
    public int findLHS(int[] nums) {
        if (nums == null || nums.length < 2) {
            return 0;
        }
        
        Map numToCount = new HashMap<>();
        for (int n : nums) {
            if (!numToCount.containsKey(n)) {
                numToCount.put(n, 0);
            }
            numToCount.put(n, numToCount.get(n) + 1);
        }
        
        int lhs = 0;
        for (int key : numToCount.keySet()) {
            if (numToCount.containsKey(key + 1)) {
                lhs = Math.max(lhs, numToCount.get(key) + numToCount.get(key + 1));
            }
        }
        
        return lhs;
    }
}