Solution Exercise 21: Python algorithm that determines the list of duplicate elements

Exercise 21

Write a Python algorithm that returns the list of duplicate elements of a given list. Example if L = [7, 23, 5, 12, 7, 19, 23, 12, 29], the algorithm returns the list: [7, 23, 12]

Solution

def listDuplicate (L):
     # initialize the list of duplicate elements
     duplicate = []
     for x in L:
          if L.count (x)> 1 and x not in duplicate:
               duplicate.append (x)
     return duplicate
#Example
L = [7, 23, 5, 12, 7, 19, 23, 12, 29]

print ("the list of duplicate elements of L is:", listDuplicate (L))
# The output is: the list of duplicate elements of L is: [7, 23, 12]