How to use a single for loop In Python

Method 1: Using the Brute Force approach

Python3 # 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...

Method 2: Using a single for loop

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Method 3: Using Counter() function from collection module

Python3 # Python program to print duplicates from # a list of integers lis = [1, 2, 1, 2, 3, 4, 5, 1, 1, 2, 5, 6, 7, 8, 9, 9]   uniqueList = [] duplicateList = []   for i in lis:     if i not in uniqueList:         uniqueList.append(i)     elif i not in duplicateList:         duplicateList.append(i)   print(duplicateList)...

Method 4: Using count() method

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Method 5: Using list comprehension method

Python3 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)...

Method 6: Using list-dictionary approach (without any inbuild count function)

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Method 7: Using in, not in operators and count() method

Python3 # 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...