POTD Solutions | 05 Nov’ 23 | Top K Frequent Elements in Array

Given a non-empty array nums[] of integers of length N, find the top k elements which have the highest frequency in the array. If two numbers have same frequencies, then the larger number should be given more preference.

Example:

Input: N = 6, nums = {1,1,1,2,2,3}, k = 2
Output: {1, 2}
Explanation: The most frequent element in nums[] is 1 and the second most frequent element is 2.

Input: N = 8, nums = {1,1,2,2,3,3,3,4}, k = 2
Output: {3, 2}
Explanation: Element 3 is the most frequent. Elements 1 and 2 have the same frequency ie. 2. Therefore, in this case, the answer includes the element 2 as 2 > 1.

Create a Map to store element-frequency pair. Map is used to perform insertion and updates in constant time. Then use a priority queue to store the element-frequency pair (Max-Heap). The element which has maximum frequency, comes at the root of the Priority Queue. Remove the top or root of Priority Queue K times and print the element.

Steps-by-step approach:

• Create a map mp, to store key-value pair, i.e. element-frequency pair.
• Traverse the array from start to end.
• For every element in the array update mp[array[i]]++
• Store the element-frequency pair in a Priority Queue
• Run a loop k times, and in each iteration remove the root of the priority queue and print the element.

Below is the implementation of the above approach: