Solution Exercise 22: List of duplicate elements without using the count() method

Exercise 22

Write an algorithm in python that returns the list of duplicate elements of a given list without using any predefined functions in Python. Example if L = [7, 23, 5, 12, 7, 19, 23, 12, 29], the algorithm returns the list [7, 23, 12].

Solution

def listDuplicate (L):
     # initialization of the list of duplicate elements
     duplicateElements = []
    
     for x in L:
         # initialize the occurrence of x in L
          occ_x = 0
          for y in L:
               if x == y:
                    occ_x = occ_x + 1
                
         # test if x is a duplicate element and add it to the duplicateElements list
          if occ_x >= 2 and x not in duplicateElements:
               duplicateElements.append (x)
    
     return duplicateElements

#Example
L = [7, 23, 5, 12, 7, 19, 23, 12, 29]
print (listDuplicate (L)) # the output is: [7, 23, 12]