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Python | Check if all elements in a List are same

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Given a list, write a Python program to check if all the elements in the given list are the same. 

Example:

Input: ['Geeks', 'Geeks', 'Geeks', 'Geeks', ]
Output: Yes
Input: ['Geeks', 'Is', 'all', 'Same', ]
Output: No

There are various ways we can do this task. Let’s see different ways we can check if all elements in a List are the same. 

Method #1: Comparing each element. 

Python3

# Python program to check if all
# elements in a List are same
 
 
def checkList(lst):
 
    ele = lst[0]
    chk = True
 
    # Comparing each element with first item
    for item in lst:
        if ele != item:
            chk = False
            break
 
    if (chk == True):
        print("Equal")
    else:
        print("Not equal")
 
 
# Driver Code
lst = ['Geeks', 'Geeks', 'Geeks', 'Geeks', ]
checkList(lst)

                    

Output
Equal

But In Python, we can do the same task in many interesting ways. 

Method #2: Using all() method 

Python3

# Python program to check if all
# elements in a List are same
res = False
 
 
def chkList(lst):
    if len(lst) < 0:
        res = True
    res = all(ele == lst[0] for ele in lst)
 
    if(res):
        print("Equal")
    else:
        print("Not equal")
 
 
# Driver Code
lst = ['Geeks', 'Geeks', 'Geeks', 'Geeks']
chkList(lst)

                    

Output
Equal

Method #3: Using count() method 

Python3

# Python program to check if all
# elements in a List are same
res = False
 
 
def chkList(lst):
    if len(lst) < 0:
        res = True
    res = lst.count(lst[0]) == len(lst)
 
    if(res):
        print("Equal")
    else:
        print("Not equal")
 
 
# Driver Code
lst = ['Geeks', 'Geeks', 'Geeks', 'Geeks']
chkList(lst)

                    

Output
Equal

  Method #4: Using set data structure Since we know there cannot be duplicate elements in a set, we can use this property to check whether all the elements are same or not. 

Python3

# Python program to check if all
# elements in a List are same
 
 
def chkList(lst):
    return len(set(lst)) == 1
 
 
# Driver Code
lst = ['Geeks', 'Geeks', 'Geeks', 'Geeks']
 
if chkList(lst) == True:
    print("Equal")
else:
    print("Not Equal")

                    

Output
Equal

Method #5 : Using len() method

Python3

# Python program to check if all
# elements in a List are same
lst = ['Geeks', 'Geeks', 'Geeks', 'Geeks']
if([lst[0]]*len(lst) == lst):
    print("Equal")
else:
    print("Not equal")

                    

Output
Equal

Method#6: Using recursion

Python3

#Python program to check if all the elements in the given list are the same.
def checkList(lst, ele=None, index=0):
    # if ele is None, assign the first element of the list to ele
    if ele is None:
        ele = lst[0]
    # base case: if index is equal to the length of the list, return True
    if index == len(lst):
        return True
    # if the current element at index is not equal to ele, return False
    elif lst[index] != ele:
        return False
    # otherwise, call the function again with the next index
    else:
        return checkList(lst, ele, index+1)
 
# Driver Code
lst = ['Geeks', 'Geeks', 'Geeks', 'Geeks']
# check if the function returns True
if checkList(lst):
    print("Equal")
else:
    print("Not equal")
 
#This code is contributed Vinay Pinjala.

                    

Output
Equal

Time Complexity: O(n)
Auxiliary Space: O(n)

Method #7: Using the reduce function from the functools library and the operator module:

Python3

from functools import reduce
import operator
 
def all_elements_same(lst):
    return reduce(operator.eq, lst)
 
# driver code
lst = [1,1,1,1,1]
if all_elements_same(lst):
    print("Equal")
else:
    print("Not Equal")

                    

Output:

Equal

Time Complexity: O(n)
Auxiliary Space: O(n)

Method #8 : Using operator.countOf() method

  1. Check whether count of first element is equal to length of list using operator.countOf()
  2. If True then all elements of list are equal Display Equal
  3. If False then Display Not equal

Python3

# Python program to check if all
# elements in a List are same
import operator
res = False
 
 
def chkList(lst):
    if len(lst) < 0:
        res = True
    res = operator.countOf(lst, lst[0]) == len(lst)
    if(res):
        print("Equal")
    else:
        print("Not equal")
 
 
# Driver Code
lst = ['Geeks', 'Geeks', 'Geeks', 'Geeks']
chkList(lst)

                    

Output
Equal

Time Complexity: O(n) n – length of list 
Auxiliary Space: O(1)

Method #9: Using  heapq module:

  1. Import the heapq module.
  2. Define the all_elements_same function which takes a list as an argument.
  3. Use the nsmallest function from heapq to find the smallest len(lst) elements in the list and check if all the elements found are equal to the first element of the list using all() functions. If it is True, print “Equal“, else print “Not Equal“.

Below is the implementation of the above approach:

Python3

# Python program for the above approach
import heapq
 
# Function to check if all elements
# are same or not
def all_elements_same(lst):
    return all(x == lst[0] for x in heapq.nsmallest(len(lst), lst))
 
 
# Driver Code
lst = [1, 1, 1, 1, 1]
if all_elements_same(lst):
    print("Equal")
else:
    print("Not Equal")
 
# This code is contributed by Rayudu

                    

Output
Equal

Time Complexity: The time complexity of this algorithm is O(N log N), where N is the length of the input list. This is because the nsmallest function uses a heap to find the smallest elements, which has a time complexity of O(N log N).

Space Complexity: The space complexity of this algorithm is O(N), where N is the length of the input list. This is because the nsmallest function creates a heap of size n to store the smallest elements. Additionally, the generator expression used in all functions also requires O(N) space.
 



Last Updated : 05 Apr, 2023
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