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Top K Frequent Elements in an Array

Certification: Intermediate Level Accuracy: 0% Submissions: 0 Points: 15

Write a C program to find the k most frequent elements in an array. Given an integer array and an integer k, return the k most frequent elements. The answer can be in any order.

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

    •  Step 1: Count frequency of each element: 1 appears 3 times, 2 appears 2 times, 3 appears 1 time.

    •  Step 2: The two most frequent elements are 1 and 2.

    •  Step 3: Return [1,2] as the result.
    •
Example 2
    
  
  • Input: nums = [1], k = 1
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  • Output: [1]
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  • Explanation:

    •  Step 1: There is only one element in the array.

    •  Step 2: Element 1 appears 1 time.

    •  Step 3: Return [1] as it's the most frequent (and only) element.
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Constraints
    
  
  • 1 ≤ nums.length ≤ 10^5
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  • -10^4 ≤ nums[i] ≤ 10^4
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  • k is in the range [1, the number of unique elements in the array]
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  • Time Complexity: O(n log k)
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  • Space Complexity: O(n)
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Hint
Solution

Solution Hints

    
  
  • First, count the frequency of each element using a hash map approach.
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  • Use arrays to store unique elements and their frequencies.
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  • Sort the elements based on their frequencies in descending order.
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  • Take the first k elements from the sorted array.
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  • Return the k most frequent elements.
    •

Steps to solve by this approach:

 Step 1: Create a structure to hold element and its frequency.
 Step 2: Count the frequency of each unique element in the input array.
 Step 3: Store unique elements and their frequencies in an array of structures.
 Step 4: Sort the array by frequency in descending order using qsort.
 Step 5: Create result array and copy the first k elements from sorted array.
 Step 6: Set the return size to k and return the result array.
 Step 7: Free allocated memory in the main function after use.

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