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Program to print N minimum elements from list of integers
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Program to print duplicates from a list of integers in Python

Last Updated : 27 Dec, 2024
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In this article, we will explore various methods to print duplicates from a list of integers in Python. The simplest way to do is by using a set.

Using Set

Set in Python only stores unique elements. So, we loop through the list and check if the current element already exist (duplicate) in the set, if true then keep this element to duplicate list. Otherwise, add element to set.

Python 
a = [1, 2, 3, 1, 2, 4, 5, 6, 5]  # Initialize an empty set to store seen elements s = set()  # List to store duplicates dup = []  for n in a:     if n in s:         dup.append(n)     else:         s.add(n)  print(dup)

Output
[1, 2, 5]

Explanation:

  • The seen set tracks the numbers we’ve already encountered.
  • If a number is found in seen then it is added to the duplicates list.

Note: This approach is efficient because checking membership in a set is O(1) on average.

Let’s explore other different ways to print duplicates from a list of integers:

Table of Content

  • Using Nested Loops (Not Efficient)
  • Using a Dictionary

Using Nested Loops (Not Efficient)

In this approach, we use two nested loops. The outer loop picks an element from the list and the inner loop compares it with every other element to see if it matches. If a match is found then it’s considered a duplicate.

Python 
a = [1, 2, 3, 1, 2, 4, 5, 6, 5]  # List to store duplicates dup = []  # Compare each element with other elements for i in range(len(a)):     for j in range(i + 1, len(a)):          # If a duplicate is found and not already recorded         if a[i] == a[j] and a[i] not in dup: 			             # Add to duplicates list             dup.append(a[i])   print(dup)

Output
[1, 2, 5]

Using a Dictionary

This method uses a dictionary to count how many times each element appears in the list. If an element appears more than once then it is a duplicate.

Python 
a = [1, 2, 3, 1, 2, 4, 5, 6, 5]  # Initialize a dictionary to count occurrences d = {}  for n in a:     d[n] = d.get(n, 0) + 1  # Find duplicates by filtering numbers with count > 1 dup = [n for n, c in d.items() if c > 1]  print(dup)

Output
[1, 2, 5]

Explanation:

  • The d dictionary counts the occurrences of each number.
  • We then filter out the numbers with a count greater than 1 to find the duplicates.

Note: This approach also has O(n) time complexity due to dictionary operations.



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Program to print N minimum elements from list of integers

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