top_k_frequent elements.cpp

/*
Given an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order.

 

Example 1:

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

Output: [1,2]

Example 2:

Input: nums = [1], k = 1

Output: [1]

Example 3:

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

Output: [1,2]

*/

class Solution {
public:
    vector<int> topKFrequent(vector<int>& nums, int k) {
        // Hash map to count frequencies of each number
        unordered_map<int, int> freq;

        // Count frequencies
        for (int& num : nums)
            freq[num]++; // Increment frequency count for each number

        priority_queue<pair<int, int>, vector<pair<int, int>>,
                       greater<pair<int, int>>>
            minHeap;
        for (auto& pair : freq) {
            int num = pair.first;
            int count = pair.second;
            minHeap.push({count, num});
            if (minHeap.size() > k)
                minHeap.pop();
        }

        vector<int> result;
        while (!minHeap.empty()) {
            result.push_back(minHeap.top().second);
            minHeap.pop();
        }

        return result;
    }
};