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Most Frequent Element in a List

Certification: Basic Level Accuracy: 79.49% Submissions: 39 Points: 5

Write a Python program that finds the most frequent element in a list.

Example 1
    

  • Input: lst = [1, 3, 2, 3, 4, 1, 3]
    • 

  • Output: 3
    • 

  • Explanation: 
      

    • Step 1: Create a dictionary to count the frequency of each element in the list.
      • 

    • Step 2: Element 1 appears twice, add entry {1: 2}.
      • 

    • Step 3: Element 3 appears three times, add entry {3: 3}.
      • 

    • Step 4: Element 2 appears once, add entry {2: 1}.
      • 

    • Step 5: Element 4 appears once, add entry {4: 1}.
      • 

    • Step 6: Find the element with the maximum frequency, which is 3.
      • 

    • Step 7: Return 3 as the most frequent element.
      • 

    •
Example 2
    

  • Input: lst = [5, 5, 5, 2, 2, 3]
    • 

  • Output: 5
    • 

  • Explanation: 
      

    • Step 1: Create a dictionary to count the frequency of each element in the list.
      • 

    • Step 2: Element 5 appears three times, add entry {5: 3}.
      • 

    • Step 3: Element 2 appears twice, add entry {2: 2}.
      • 

    • Step 4: Element 3 appears once, add entry {3: 1}.
      • 

    • Step 5: Find the element with the maximum frequency, which is 5.
      • 

    • Step 6: Return 5 as the most frequent element.
      • 

    •
Constraints
    

  • 1 ≤ len(lst) ≤ 10^5
    • 

  • -10^5 ≤ lst[i] ≤ 10^5
    • 

  • Time Complexity: O(n) where n is the length of the input list
    • 

  • Space Complexity: O(n) to store the frequency dictionary
    •
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Hint
Solution

Solution Hints

    
  
  • Use the collections.Counter class to count element frequencies.
    • 
  
  • Use the max() function with a custom key to find the most frequent element.
    • 
  
  • Iterate through the list and maintain a frequency map using a dictionary.
    •

Steps to solve by this approach:

 Step 1: Import the Counter class from the collections module.

 Step 2: Create a Counter object from the input list to count element occurrences.

 Step 3: Get the keys from the Counter (the unique elements).

 Step 4: Find the key with the maximum count value using a lambda function.

 Step 5: Return the most frequent element (handling ties by returning the first found).

 Step 6: Handle the case of an empty list by raising an appropriate exception.

Submitted Code :