Python: Find the closest palindrome

Last update on April 17 2025 13:02:35 (UTC/GMT +8 hours)

Closest Palindrome to String

Write a Python program to find the closest palindrome to a given string.

Input:  
cat
Output:
cac

Input:  
madan
Output:
madam
Input: 
radivider
Output:
radividar

Input: 
madan
Output:
madam
Input: 
abc
Output:
aba

Input: 
racecbr
Output:
racecar

Sample Solution:

Python Code:

# Define a function named 'test' that finds the closest palindrome of a given string 's'
def test(s):
    # Initialize a variable 'odd' to count the number of differing characters between mirrored positions
    odd = 0
    
    # Iterate through the characters of the string along with their indices
    for i, c in enumerate(s):
        # Check if the character at the current position is not equal to its mirrored position
        if c != s[~i]:
            # Increment the 'odd' count
            odd += 1
    
    # Check if the count of differing characters is an odd number
    if odd % 2 == 1:
        # Calculate the half of the 'odd' count
        half = odd // 2
        # Construct a palindrome by taking characters from the original string and its mirrored positions
        pal = "".join((s[i] if i < half else s[~i] for i in range(len(s))))
        # Return the closest palindrome
        return pal
    else:
        # Calculate the half of the 'odd' count
        half = odd // 2
        # Construct a palindrome by taking characters from the original string and its mirrored positions
        pal = "".join((s[i] if i <= half else s[~i] for i in range(len(s))))
        # Return the closest palindrome
        return pal

# Example 1
s1 = "cat"
print("Original string:", s1) 
print("Closest palindrome of the said string:")
print(test(s1))

# Example 2
s2 = "madan"
print("\nOriginal string:", s2) 
print("Closest palindrome of the said string:")
print(test(s2))

# Example 3
s3 = "radivider"
print("Original string:", s3) 
print("Closest palindrome of the said string:")
print(test(s3))

# Example 4
s4 = "madan"
print("\nOriginal string:", s4) 
print("Closest palindrome of the said string:")
print(test(s4)) 

# Example 5
s5 = "abc"
print("Original string:", s5) 
print("Closest palindrome of the said string:")
print(test(s5))

# Example 6
s6 = "racecbr"
print("\nOriginal string:", s6) 
print("Closest palindrome of the said string:")
print(test(s6))

Sample Output:

Original string: cat
Closest palindrome of the said string:
cac

Original string: madan
Closest palindrome of the said string:
madam
Original string: radivider
Closest palindrome of the said string:
radividar

Original string: madan
Closest palindrome of the said string:
madam
Original string: abc
Closest palindrome of the said string:
aba

Original string: racecbr
Closest palindrome of the said string:
racecar

Flowchart:

For more Practice: Solve these Related Problems:

Write a Python program to find the palindrome closest to a given string by mirroring its first half.
Write a Python program to transform a string into a palindrome by minimally altering characters and return the result.
Write a Python program to compute the nearest palindrome by checking variations of the original string and selecting the closest match.
Write a Python program to implement a function that finds the closest lexicographically valid palindrome to a given input string.

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Python Code Editor :

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