Top K Frequent Elements

Top K Frequent Elements

Given a non-empty array of integers, return the k most frequent elements.

Example 1:

Input: nums = [1,1,1,2,2,3], k = 2
Output: [1,2]

Example 2:

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

Note:

• You may assume k is always valid, 1 ≤ k ≤ number of unique elements.

• Your algorithm's time complexity must be better than O(n log n), where n is the array's size.

• It's guaranteed that the answer is unique, in other words the set of the top k frequent elements is unique.

• You can return the answer in any order.

Solutions

🧠 Cpp

#include <map>

class Solution
{
public:
    vector<int> topKFrequent(vector<int>& nums, int k)
    {
        std::map<int, int> input_map;
        for(int i : nums)
            input_map[i]++;

        //sort by values(freqency)
        std::multimap<int, int> sorted_input_map;
        for(auto p : input_map)
            sorted_input_map.insert({p.second, p.first});

        vector<int> res;
        for(auto iter = --sorted_input_map.end(); k--; --iter)
            res.push_back(iter->second);

        return res;
    }
};