Python: Find the closest palindrome

Last update on May 28 2022 13:41:34 (UTC/GMT +8 hours)

Python Programming Puzzles: Exercise-93 with Solution

Write a Python program to find the closest palindrome from 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:

#License: https://bit.ly/3oLErEI

def test(s):
    odd = 0
    for i, c in enumerate(s):
        if c != s[~i]:
            odd += 1
    if odd % 2 == 1:
        half = odd // 2
        pal = "".join((s[i] if i < half else s[~i] for i in range(len(s))))
        return pal
    else:
        half = odd // 2
        pal = "".join((s[i] if i <= half else s[~i] for i in range(len(s))))
        return pal

s = "cat"
print("Original string:",s) 
print("Closest palindrome of the said string:")
print(test(s))
s = "madan"
print("\nOriginal string:",s) 
print("Closest palindrome of the said string:")
print(test(s))
s = "radivider"
print("Original string:",s) 
print("Closest palindrome of the said string:")
print(test(s))
s = "madan"
print("\nOriginal string:",s) 
print("Closest palindrome of the said string:")
print(test(s)) 
s = "abc"
print("Original string:",s) 
print("Closest palindrome of the said string:")
print(test(s))
s = "racecbr"
print("\nOriginal string:",s) 
print("Closest palindrome of the said string:")
print(test(s))

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:

Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Python Code Editor :

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Python: Tips of the Day

Find current directory and file's directory:

To get the full path to the directory a Python file is contained in, write this in that file:

import os dir_path = os.path.dirname(os.path.realpath(__file__))

(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)

To get the current working directory use

import os cwd = os.getcwd()

Documentation references for the modules, constants and functions used above:

The os and os.path modules.

The __file__ constant

os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")

os.path.dirname(path) (returns "the directory name of pathname path")

os.getcwd() (returns "a string representing the current working directory")

os.chdir(path) ("change the current working directory to path")

Ref: https://bit.ly/3fy0R6m