Longest Harmonious Subsequence in C++

Suppose we have an integer array; we have to find the length of its longest harmonious subsequence among all its possible subsequences. As we know a harmonious sequence array is an array where the difference between its maximum value and its minimum value is exactly 1.

So, if the input is like [1,3,2,2,5,2,3,7], then the output will be 5, as the longest harmonious subsequence is [4,3,3,3,4].

To solve this, we will follow these steps −

• Define one map m

• for n in nums −

  • (increase m[n] by 1)

• for key-value pair (k,v) in m −

  • it := position of (k+1) in m

  • if 'it' is in m, then −

    • max_:= maximum of max_ and value of it

• return max_

Example 

Let us see the following implementation to get a better understanding −

 Live Demo

#include <bits/stdc++.h> using namespace std; class Solution { public:    int findLHS(vector<int>& nums) {       unordered_map<int, int> m;       for (const int n : nums)          ++m[n];       int max_{ 0 };       for (const auto & [ k, v ] : m) {          auto it = m.find(k + 1);          if (it != m.end())             max_ = max(max_, v + it->second);       }       return max_;    } }; main(){    Solution ob;    vector<int> v = {2,4,3,3,6,3,4,8};    cout << (ob.findLHS(v)); }

Input

{2,4,3,3,6,3,4,8}

Output

5