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Home Interviews Find duplicate elements in a list – MindStick
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1 Answers

ICSM Computer
ICSM Computer 10 Sep 2025
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Using Counter :

from collections import Counter

nums = [1, 2, 3, 2, 4, 5, 1, 6, 3]

counts = Counter(nums)
duplicates = [item for item, count in counts.items() if count > 1]

print("Duplicates:", duplicates)

Output:

Duplicates: [1, 2, 3]

Using Set :

def find_duplicates(nums):
    seen = set()
    duplicates = set()
    for n in nums:
        if n in seen:
            duplicates.add(n)
        else:
            seen.add(n)
    return list(duplicates)

print(find_duplicates([1, 2, 3, 2, 4, 5, 1, 6, 3]))

Answer: (order may vary)

[1, 2, 3]

Explanation:

  • Keep track of numbers in seen.
  • If already in seen, move to duplicates.

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