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Top K Frequent Elements

Certification: Advanced Level Accuracy: 0% Submissions: 0 Points: 10

Write a C# program to find the k most frequent elements in an array. Return the answer 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: The elements 1 and 2 appear most frequently. 1 occurs 3 times and 2 occurs 2 times.
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Example 2
    
  
  • Input: nums = [1], k = 1
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  • Output: [1]
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  • Explanation: There's only one element, so it's the most frequent by default.
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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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  • It is guaranteed that the answer is unique
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  • Time Complexity: O(n log n)
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  • Space Complexity: O(n)
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Hint
Solution

Solution Hints

    
  
  • Use a dictionary to count the frequency of each element
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  • Consider using a priority queue (heap) to find the k most frequent elements
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  • Alternatively, use bucket sort for O(n) time complexity
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  • Sort the elements based on their frequency
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  • Return the top k elements
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Steps to solve by this approach:

 Step 1: Create a dictionary to count the frequency of each element in the array.
 Step 2: Create an array of lists (buckets) where the index represents the frequency.
 Step 3: Iterate through the frequency map and add each number to the corresponding bucket.
 Step 4: Iterate through the buckets from highest frequency to lowest.
 Step 5: Add elements from each bucket to the result list until we have k elements.
 Step 6: Return the result list converted to an array.
 Step 7: This bucket sort approach gives us O(n) time complexity.

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