Python | Programa para imprimir duplicados de una lista de enteros

Dada una lista de enteros con elementos duplicados en ella. La tarea de generar otra lista, que contiene solo los elementos duplicados. En palabras simples, la nueva lista debe contener los elementos que aparecen en más de uno.

Ejemplos: 

Input : list = [10, 20, 30, 20, 20, 30, 40, 50, -20, 60, 60, -20, -20]
Output : output_list = [20, 30, -20, 60]


Input :  list = [-1, 1, -1, 8]
Output : output_list = [-1]

Método 1: Usar el enfoque de fuerza bruta

# Python program to print
# duplicates from a list
# of integers
def Repeat(x):
    _size = len(x)
    repeated = []
    for i in range(_size):
        k = i + 1
        for j in range(k, _size):
            if x[i] == x[j] and x[i] not in repeated:
                repeated.append(x[i])
    return repeated
 
# Driver Code
list1 = [10, 20, 30, 20, 20, 30, 40,
         50, -20, 60, 60, -20, -20]
print (Repeat(list1))
     
# This code is contributed
# by Sandeep_anand

[20, 30, -20, 60]

Método 2: Usar la función Counter() del módulo de colección

from collections import Counter
 
l1 = [1,2,1,2,3,4,5,1,1,2,5,6,7,8,9,9]
d = Counter(l1)
print(d)
 
new_list = list([item for item in d if d[item]>1])
print(new_list)

Counter({1: 4, 2: 3, 5: 2, 9: 2, 3: 1, 4: 1, 6: 1, 7: 1, 8: 1})
[1, 2, 5, 9]

Método 3: Usando el método count()

# program to print duplicate numbers in a given list
# provided input
list = [1, 2, 1, 2, 3, 4, 5, 1, 1, 2, 5, 6, 7, 8, 9, 9]
 
new = []  # defining output list
 
# condition for reviewing every
# element of given input list
for a in list:
 
     # checking the occurrence of elements
    n = list.count(a)
 
    # if the occurrence is more than
    # one we add it to the output list
    if n > 1:
 
        if new.count(a) == 0:  # condition to check
 
            new.append(a)
 
print(new)
 
# This code is contributed by Himanshu Khune

[1, 2, 5, 9]

Método 4: Usar el método de comprensión de listas

def duplicate(input_list):
    return list(set([x for x in input_list if input_list.count(x) > 1]))
 
if __name__ == '__main__':
    input_list = [1, 2, 1, 2, 3, 4, 5, 1, 1, 2, 5, 6, 7, 8, 9, 9]
    print(duplicate(input_list))
 
# This code is contributed by saikot

[1, 2, 5, 9]

Método 5: usar el enfoque de diccionario de lista (sin ninguna función de conteo incorporada)

def duplicate(input_list):
    new_dict, new_list = {}, []
 
    for i in input_list:
        if not i in new_dict:
            new_dict[i] = 1
        else:
            new_dict[i] += 1
 
    for key, values in new_dict.items():
        if values > 1:
            new_list.append(key)
 
    return new_list
 
if __name__ == '__main__':
    input_list = [1, 2, 1, 2, 3, 4, 5, 1, 1, 2, 5, 6, 7, 8, 9, 9]
    print(duplicate(input_list))
 
# This code is contributed by saikot

[1, 2, 5, 9]

Método 6: Usar operadores in, not in y el método count()

lis = [1, 2, 1, 2, 3, 4, 5, 1, 1, 2, 5, 6, 7, 8, 9, 9]
x = []
y = []
for i in lis:
    if i not in x:
        x.append(i)
for i in x:
    if lis.count(i) > 1:
        y.append(i)
print(y)

[1, 2, 5, 9]