Top K Frequent Elements LeetCode Solution

Difficulty Level Medium
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Problem Statement

Top K Frequent Elements LeetCode Solution Says that – 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]

 

Constraints:

  • 1 <= nums.length <= 105
  • k is in the range [1, the number of unique elements in the array].
  • It is guaranteed that the answer is unique.

 

Algorithm:

Idea:

  • In order to find the Top k Frequent Elements. First, we will focus on the frequency of each element present in an array.
  • After finding the Frequency of Each element we will make one maximum heap and push all elements into the heap with their Frequency.
  • At last, we will make one result list and will pop out the k element from the heap and append that element into the result and return the result.

Approach:

  • At first, We will make one Hashmap and will traverse through the whole array and set the frequency of each element as value and element as Key in the Hashmap.
  • After that, we will make one priority queue(maxheap) and again traverse through the whole array and push all the elements as tuple pairs (-value, key) into the maxheap.
  • Then, we will run a loop from 0 to K and pop out the elements from maxheap and append the Key of each tuple into the result and return the result.
  • Hence We will find the Top K frequent Elements.

Top K Frequent Elements LeetCode Solution

class Solution:
    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
        dic = {}
        
        for i in nums:
            if i in dic:
                dic[i] += 1
                
            else:
                dic[i] = 1
        
        max_heap = []
        for i in dic:
            heapq.heappush(max_heap,(-dic[i],i))
            
        result = []
        for i in range(k):
            result.append(heapq.heappop(max_heap)[1])
        
        return result
        
            
        
        
class Solution {
    public int[] topKFrequent(int[] nums, int k) {
        
      Map<Integer, Integer> dic = new HashMap<>();
        for(int num : nums){ dic.put(num, dic.getOrDefault(num, 0) + 1); }
        
        Queue<Integer> max_heap = new PriorityQueue<>((a, b) -> dic.get(b) - dic.get(a));
        for(int key : dic.keySet()){ max_heap.add(key); }
        
        int[] result = new int[k];
        for(int i = 0; i < k; i++){
            result[i] = max_heap.poll();
        }
        
        return result;
    } 
}

Complexity Analysis of Top K Frequent Elements Leetcode Solution:

Time complexity:

The Time Complexity of the above solution is O(nlogn) where n = the size of the input array. We have traversed the entire array and for each element, we are doing the heapify operation.

Space complexity:

The Space Complexity of the above solution is O(n) since we are creating a max heap of size n.

SIMILAR QUESTION                 https://leetcode.com/problems/word-frequency/

https://leetcode.com/problems/kth-largest-element-in-an-array/

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