Python program to check whether number formed by combining all elements of the array is palindrome

Given an array arr[], the task is to combine all the elements in the array sequentially and check if it is a palindrome.

Examples:

Input: arr[] ={1 , 69 , 54 , 45 , 96 , 1}

Output: palindrome

Explanation: The number formed by combining all the elements is “1695445961” which is a palindrome

Input: arr[] ={2 , 73 , 95 , 59 , 96 , 2}

Output: not palindrome

Explanation: The number formed by combining all the elements is “2739559962” which is not a palindrome

Method 1: Using map() and join()

• Convert each element of the list to a string using map() function.
• Join the list using join() function.
• Check if it is a palindrome.
• If yes then print palindrome.
• If no print, not a palindrome.

Below is the implementation of the above approach:

Python3

# function to check palindrome
def checkPalindrome(string):

    # reverse the string
    rev = string[::-1]

    # checking if string is equal to reverse
    if(string == rev):
        return True
    else:
        return False

# function to convert list to single number string


def joinArray(lis):

    # convert the elements of list to string
    lis = list(map(str, lis))

    # converting list to string
    number = ''.join(lis)

    # checking if it is palindrome
    if(checkPalindrome(number)):
        return True
    else:
        return False


# Driver code
lis = [1, 76, 39, 93, 67, 1]
if(joinArray(lis)):
    print("Palindrome")
else:
    print("not Palindrome")

Output

Palindrome

Time Complexity: O(n) 

Method 2: Using type casting and string concatenation

• Take an empty string say str.
• Traverse through the list and convert each element to string using type casting
• Add this to str using string concatenation
• Check if str is a palindrome

Below is the implementation of the above approach:

Python3

# function to check palindrome
def checkPalindrome(string):

    # reverse the string
    rev = string[::-1]

    # checking if string is equal to reverse
    if(string == rev):
        return True
    else:
        return False

# function to convert list to single number string


def joinArray(lis):

    # defining empty string as number
    number = ""

    # convert the elements of list to string using type conversion
    for i in lis:

        # converting to string
        i = str(i)

        # concat this to string
        number = number + i

    # checking if it is palindrome
    if(checkPalindrome(number)):
        return True
    else:
        return False


# Driver code
lis = [1, 76, 39, 93, 67, 1]

if(joinArray(lis)):
    print("Palindrome")
else:
    print("not Palindrome")

Output

Palindrome

Method 3 : Using str(),list(),extend(),join() and reverse() methods

Python3

lis = [1, 76, 39, 93, 67, 1]
s = ""
for i in lis:
    s += str(i)
x = list(s)
y = []
y.extend(x)
x.reverse()
if(x == y):
    print("Palindrome")
else:
    print("not Palindrome")

Output

Palindrome

Method 4 : Using reduce():

Algorithm:

1. Import the “reduce” function from the “functools” module.
2. Create a list of integers “lst”.
3. Use the “reduce” function to concatenate all the integers in the list into a single string “s”.
4. Check whether the string “s” is equal to its reverse.
5. If “s” is equal to its reverse, print “Palindrome”; otherwise, print “Not Palindrome”.

Python3

from functools import reduce
lst = [1, 76, 39, 93, 67, 1]
# concatenate all numbers into a single string
s = reduce(lambda x, y: str(x) + str(y), lst)
# compare string with its reverse
if s == s[::-1]:
    print("Palindrome")
else:
    print("Not Palindrome")

    #This code is contributed by Jyothi Pinjala.

Output

Palindrome

Time complexity: O(n), where n is the number of integers in the list “lst”. This is because the reduce function takes O(n) time to concatenate all the integers into a single string, and checking whether the string is equal to its reverse takes O(n/2) time.
Auxiliary Space: O(n), where n is the number of integers in the list “lst”. This is because the reduce function creates a new string of length n by concatenating all the integers in the list.