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# Discover Longest Palindrome in a Python String (Straightforward) – Finxter

## Coding Problem

💬 Problem: Given a string. Learn how to discover the longest palindrome within the string?

For comprehensibility, enable me to rapidly add a definition of the time period palindrome:

💡 Definition: A palindrome is a sequence of characters that reads the identical backward as ahead equivalent to `'madam'`, `'anna'`, or `'101'`.

This text needs to provide you a fast and straightforward answer in Python. First, we’ll resolve the better however vital drawback of checking if a substring is a palindrome within the first place:

## Verify If Substring is Palindrome

You may simply test if a substring is a palindrome through the use of the slicing expression `phrase == phrase[::-1]` that evaluates to `True` if the phrase is similar ahead and backward, i.e., it’s a palindrome.

👉 Really useful Tutorial: Python Palindromes One-Liner

Subsequent, we’ll discover discover the longest substring in a Python string that can be a Palindrome. Yow will discover our palindrome checker within the code answer (highlighted):

## Discover Longest Substring That’s Palindrome

The brute-force method to discovering the longest palindrome in a string is to iterate over all substrings in a nested `for` loop. Then test every substring if it’s a palindrome utilizing `phrase == phrase[::-1]`. Preserve monitor of the longest palindrome utilizing the `len()` operate in an `if` situation.

```def find_longest_palindrome(s):
longest=""
n = len(s)
for i in vary(n):
for j in vary(i+1,n+1):
phrase = s[i:j]
if phrase == phrase[::-1]:
if len(phrase)>len(longest):
longest = phrase
return longest

print(find_longest_palindrome('anna'))
# anna

print(find_longest_palindrome('abc'))
# a
```

## Runtime Complexity

This has cubic runtime complexity, i.e., for a string with size `n`, we have to test `O(n*n)` completely different phrases. Every phrase could have as much as `n` characters, thus the palindrome test itself is `O(n)`. Collectively, this yields runtime complexity of `O(n*n*n) = O(n³)`.

## Dialogue and Higher Options

Is that this the perfect we will do?

No! The perfect we will theoretically do is a linear runtime complexity and linear area complexity referred to as Manacher’s Algorithm. The thought is to decide on a number of “palindrome facilities” and develop these facilities one step at a time by including characters to the left or the appropriate.

Nevertheless, you’re not anticipated to give you this your self in a coding interview.

What some interviewers could count on is to give you a “dynamic programming” concept the place you assemble a Boolean matrix.

Knowledge Construction: Every cell `(i,j)` of the Boolean Matrix is `True` if the string `s[i:j]` is a Palindrome and `False` in any other case. The cell that’s `True` and has the best worth for `j-i` represents the longest Palindrome.

Algorithm: Fill the info construction with Boolean values. You may assemble a cell `(i,j)` from the smaller cells simply by checking if the smaller substring `s[i+1:j-1]` is a Palindrome and the primary and final characters `s[i]` and `s[j]` are the identical. Set the cell to `False` or `True` accordingly. Initialize the info construction with diagonal values `(i,i) == True`.

Word we do NOT use Python indexing on this description, i.e., the tip index of a slice is included.

Right here’s a fast overview of this concept:

🧩 Train: Implement this concept in Python code and send it to me!

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