Python program to check whether the string is Symmetrical or Palindrome

Given a string. the task is to check if the string is symmetrical and palindrome or not. A string is said to be symmetrical if both the halves of the string are the same and a string is said to be a palindrome string if one half of the string is the reverse of the other half or if a string appears same when read forward or backward.

Example:

Input: khokho
Output: 
The entered string is symmetrical
The entered string is not palindrome

Input:amaama
Output:
The entered string is symmetrical
The entered string is palindrome

Approach 1: The approach is very naive. In the case of palindrome, a loop is run to the mid of the string and the first and last characters are matched. If the characters are not similar then the loop breaks and the string is not palindrome otherwise the string is a palindrome. In the case of symmetry, if the string length is even then the string is broken into two halves and the loop is run, checking the characters of the strings of both the half. If the characters are not similar then the loops break and the string is not symmetrical otherwise the string is symmetrical. If the string length is odd then the string is broken into two halves in such a way that the middle element is left unchecked, and the above same step is repeated.

Below is the implementation.

Python3

# Python program to demonstrate
# symmetry and palindrome of the
# string


# Function to check whether the
# string is palindrome or not
def palindrome(a):

    # finding the mid, start
    # and last index of the string
    mid = (len(a)-1)//2     #you can remove the -1 or you add <= sign in line 21
    start = 0                #so that you can compare the middle elements also.
    last = len(a)-1
    flag = 0

    # A loop till the mid of the
    # string
    while(start <= mid):

        # comparing letters from right
        # from the letters from left
        if (a[start]== a[last]):

            start += 1
            last -= 1

        else:
            flag = 1
            break;

    # Checking the flag variable to
    # check if the string is palindrome
    # or not
    if flag == 0:
        print("The entered string is palindrome")
    else:
        print("The entered string is not palindrome")

# Function to check whether the
# string is symmetrical or not
def symmetry(a):

    n = len(a)
    flag = 0

    # Check if the string's length
    # is odd or even
    if n%2:
        mid = n//2 +1
    else:
        mid = n//2

    start1 = 0
    start2 = mid

    while(start1 < mid and start2 < n):

        if (a[start1]== a[start2]):
            start1 = start1 + 1
            start2 = start2 + 1
        else:
            flag = 1
            break

    # Checking the flag variable to
    # check if the string is symmetrical
    # or not
    if flag == 0:
        print("The entered string is symmetrical")
    else:
        print("The entered string is not symmetrical")

# Driver code
string = 'amaama'
palindrome(string)
symmetry(string)

Output

The entered string is palindrome
The entered string is symmetrical

Approach 2:

We use slicing in this method.

Python3

string = 'amaama'
half = int(len(string) / 2)

if len(string) % 2 == 0:  # even
    first_str = string[:half]
    second_str = string[half:]
else:  # odd
    first_str = string[:half]
    second_str = string[half+1:]

# symmetric
if first_str == second_str:
    print(string, 'string is symmetrical')
else:
    print(string, 'string is not symmetrical')

# palindrome
if first_str == second_str[::-1]:  # ''.join(reversed(second_str)) [slower]
    print(string, 'string is palindrome')
else:
    print(string, 'string is not palindrome')

Output

amaama string is symmetrical
amaama string is palindrome

The Time and Space Complexity for all the methods are the same:

Time Complexity: O(n)

Auxiliary Space: O(n)