Check If Number Formed by Array is Palindrome in Python

In python an array(list) of comma-separated values (items) enclosed in square brackets is one of the most flexible data types available in Python. The fact that a list's elements do not have to be of the same type is important.

In this article, we will learn a python program to check whether a number formed by combining all elements of the array is a palindrome.

Methods Used

The following are the various methods to accomplish this task:

• Using map() & join() functions

• Using type casting & string concatenation

• Using str(), list(), extend(), join() and reverse() functions

Example

Assume we have taken an input list. We will now check whether the number formed by combining all elements of the list is a palindrome or not using the above methods.

Input

inputList = [3, 25, 42, 24, 52, 3]

Output

Yes, it is a Palindrome

In the above example, all the input list elements are combined to form a single number in string form i.e, 3254224523. This number is a palindrome. Hence the output is a palindrome

Using map() & join() functions

str() function(returns the string format of the object i.e converts into string)

join() ? join() is a string function in Python that is used to join elements of a sequence that are separated by a string separator. This function connects sequence elements to convert to a string.

list() function(converts the sequence/iterable to a list).

map() function - maps any function over an iterator/list.

Example

The following program checks whether a number formed by combining all elements of the array is a palindrome using map() and join() functions -

# creating a function to check whether the string passed to it
# is a palindrome or not
def checkingPalindrome(inputString):
    # reversing the input string
    reverseStr = inputString[::-1]
    # checking whether the input string is equal to its reverse string
    if(inputString == reverseStr):
        # returning True if the condition is true
        return True
    else:
        # else returning False
        return False
      
# creating a function to convert the input list into a string
# by accepting the input list as an argument to it.
def joiningList(inputList):
    # converting all the input list elements into a string
    inputList = list(map(str, inputList))
    # converting the input list to a string using the join() function
    resultNum = ''.join(inputList)
    # checking whether the above-converted string number is a palindrome
    # by calling the above defined checkingPalindrome() function
    if(checkingPalindrome(resultNum)):
        # returning True if the function returns True
        return True
    else:
        # else returning False
        return False
# main code
# input list
inputList = [3, 25, 42, 24, 52, 3]
# Calling the above defined joiningList() function by passing input list to it
# and checking whether the function returns True/False
if(joiningList(inputList)):
  # printing Palindrome if the joiningList() fuction returns True
    print("Yes, it is a Palindrome")
else:
  # else printing NOT a Palindrome
    print("No, it is NOT a Palindrome")

Output

On executing, the above program will generate the following output -

Yes, it is a Palindrome

Using type casting & string concatenation

The following program checks whether a number formed by combining all elements of the array is a palindrome using type casting & string concatenation -

Example

# creating a function to check whether the string passed to is
# palindrome or not
def checkingPalindrome(inputString):
    # reversing the input string
    reverseStr = inputString[::-1]
    # checking whether the input string is equal to its reverse string
    if(inputString == reverseStr):
        # returning True if the condition is true
        return True
    else:
        # else returning False
        return False

# creating a function to convert the input list into a string
# by accepting the input list as an argument to it.
def joiningList(inputList):
    # Creating an empty string for storing list elements as a number
    resultNum = ""
    # travsering through the input list
    for e in inputList:
        # converting each element of list into a string
        e = str(e)
        # adding the string element to the resultNum
        resultNum = resultNum + e
    # checking whether the above-converted string number is a palindrome
    # by calling the above defined checkingPalindrome() function
    if(checkingPalindrome(resultNum)):
        # returning True if the function returns True
        return True
    else:
        # else returning False
        return False
# input list
inputList = [3, 25, 42, 24, 52, 3]
# Calling the above defined joiningList() function by passing input list to it
# and checking whether the function returns True/False
if(joiningList(inputList)):
  # printing Palindrome if the joiningList() fuction returns True
    print("Yes, it is a Palindrome")
else:
  # else printing NOT a Palindrome
    print("No, it is NOT a Palindrome")

Output

On executing, the above program will generate the following output -

Yes, it is a Palindrome

Using str(), list(), extend(), join() and reverse() functions

extend() function(adds all the elements of an iterable like list, tuple, string etc to the end of the list)

reverse() function ? a built-in function that is used to reverse objects of the list. It simply alters the original list rather than taking up additional space.

The following program checks whether a number formed by combining all elements of the array is a palindrome using type casting & string concatenation -

Example

# input list
inputList = [3, 25, 42, 24, 52, 3]
# an empty string for storing list elements as a number
resultantStr = ""
# travsering through the input list
for e in inputList:
  # converting each element of the list as a string and adding it to the result string
    resultantStr += str(e)
# converting the result string into a list
newList = list(resultantStr)
# empty list
k = []
# extending the new list to the above empty list
k.extend(newList)
# reversing the new list
newList.reverse()
# checking whether the new list is equal to the extended list
if(newList == k):
  # printing Palindrome if the condition is True
    print("Yes, it is a Palindrome")
else:
  # Else printing NOT a Palindrome
    print("No, it is NOT a Palindrome")

Output

On executing, the above program will generate the following output -

Yes, it is a Palindrome

Conclusion

In this article we have learned how to check whether number formed by combining all elements of the array is palindrome using 3 different approaches. We also learned how to use the map() method to apply a function to every element in the list. Using the extend() function, we finally learned how to combine two lists.