Longest Palindromic Substring in DSA Python - Build from Scratch

Longest Palindromic Substring

📖 Scenario: Imagine you are building a text analysis tool that finds the longest palindrome inside a given word or sentence. A palindrome is a word or phrase that reads the same backward as forward, like "racecar" or "madam".

🎯 Goal: Build a Python program that finds the longest palindromic substring inside a given string.

📋 What You'll Learn

Create a variable to hold the input string

Create a helper function to check palindromes

Use loops to find the longest palindromic substring

Print the longest palindromic substring found

💡 Why This Matters

🌍 Real World

Finding palindromes is useful in text analysis, DNA sequence analysis, and error detection in data.

💼 Career

Understanding string manipulation and nested loops is important for software development and algorithm design.

1

Create the input string

Create a variable called input_string and set it to the exact value "babad".

DSA Python

# Create a variable called input_string with value "babad"
# Your code here

Hint

Use simple assignment like input_string = "babad".

2

Create a helper function to check palindrome

Create a function called is_palindrome that takes a string s and returns True if s is a palindrome, otherwise False. Use slicing s == s[::-1] to check.

DSA Python

input_string = "babad"
# Define function is_palindrome(s) to check if s is palindrome
# Your code here

Hint

Use def is_palindrome(s): and return s == s[::-1].

3

Find the longest palindromic substring

Create a variable longest as an empty string. Use two nested for loops with variables start and end to check every substring of input_string. If the substring input_string[start:end] is a palindrome and its length is greater than len(longest), update longest to this substring.

DSA Python

input_string = "babad"

def is_palindrome(s):
    return s == s[::-1]

# Find longest palindromic substring
# Your code here

Hint

Use nested loops to check all substrings and update longest when you find a longer palindrome.

4

Print the longest palindromic substring

Use print(longest) to display the longest palindromic substring found.

DSA Python

input_string = "babad"

def is_palindrome(s):
    return s == s[::-1]

longest = ""
for start in range(len(input_string)):
    for end in range(start + 1, len(input_string) + 1):
        substring = input_string[start:end]
        if is_palindrome(substring) and len(substring) > len(longest):
            longest = substring

# Print the longest palindrome
# Your code here

Hint

Use print(longest) to show the result.