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Python – Test if list is Palindrome

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In programming, determining if a list is a palindrome is a classic exercise that can sharpen your algorithmic thinking and Python skills. A palindrome is a sequence that remains the same even when reversed. Given a List, check if it is palindrome. 

Input: test_list = [4, 5, 4] 
Output: True 
Explanation: List is same from front and rear.

Input: test_list = [4, 5, 5] 
Output: True 
Explanation: List is not same from front and rear. 

Method 1: Using list slicing

In this, we extract the first and reverse 2nd half of the list, and then compare for equality, if found equal, then we conclude its palindrome.

Python3




# Python3 code to demonstrate working of
# Test if list is Palindrome
# Using list slicing
 
# initializing list
test_list = [1, 4, 5, 4, 1]
 
# printing original list
print("The original list is : " + str(test_list))
 
# Reversing the list
reverse = test_list[::-1]
 
# checking if palindrome
res = test_list == reverse
 
# printing result
print("Is list Palindrome : " + str(res))


Output

The original list is : [1, 4, 5, 4, 1]
Is list Palindrome : True

Time complexity: O(n)
Auxiliary space: O(n)

Method 2 : Using reversed()

In this, we simply reverse the list and check if both original list and reversed list is similar.

Python3




# Python3 code to demonstrate working of
# Test if list is Palindrome
# Using reversed()
 
# initializing list
test_list = [1, 4, 5, 4, 1]
 
# printing original list
print("The original list is : " + str(test_list))
 
# reversing list
rev_list = list(reversed(test_list))
 
# checking for Palindrome
res = rev_list == test_list
 
# printing result
print("Is list Palindrome : " + str(res))


Output

The original list is : [1, 4, 5, 4, 1]
Is list Palindrome : True

Time Complexity: O(n) where n is the number of elements in the list “test_list”.  reversed() performs n number of operations.
Auxiliary Space: O(1), no extra space is required

Method 3 : Using reverse() method

One of the best approach is to reverse the list and then compare it to the original list. If they match, the list is a palindrome.

Python3




#Using lists and reverse() method
def isPalindrome(x):
    y=[]
    y.extend(x)
    x.reverse()
    if(x==y):
        return True
    return False
 
# Driver Code
test_list = [1, 4, 5, 4, 1]
print("The original list is : " + str(test_list))
ans = isPalindrome(test_list)
if ans:
    print("Is palindrome ? "+"Yes")
 
else:
    print("Is palindrome ? "+"No")


Output

The original list is : [1, 4, 5, 4, 1]
Is palindrome ? Yes

Approach 4: Using Iterative comparision

Testing if a list is a palindrome using an iterative approach involves comparing elements from both ends of the list towards the center. Iterate through the first half of the input list.Compare the elements at the current position with their corresponding elements from the end of the list.If any pair of elements doesn’t match, return No as it’s not a palindrome.If all pairs match, return Yes indicating that the list is a palindrome.

Python3




def is_palindrome(input_list):
    length = len(input_list)
    for i in range(length // 2):
        if input_list[i] != input_list[length - i - 1]:
            return 'No'
    return 'yes'
 
test_list1 = [4, 5, 4]
test_list2 = [4, 5, 5]
 
print(is_palindrome(test_list1))
print(is_palindrome(test_list2))


Output

yes
No

Time Complexity: O(n), where n is the length of the input list.
Space Complexity: O(1), which is constant.



Last Updated : 25 Aug, 2023
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