﻿ C# - Longest Palindromic substring from a given string

C#: Get the longest Palindromic substring from a given string

C# Sharp String: Exercise-44 with Solution

Write a C# Sharp program to get the longest Palindromic substring from a given string.
From Wikipedia:
In computer science, the longest palindromic substring or longest symmetric factor problem is the problem of finding a maximum-length contiguous substring of a given string that is also a palindrome. For example, the longest palindromic substring of "bananas" is "anana". The longest palindromic substring is not guaranteed to be unique; for example, in the string "abracadabra", there is no palindromic substring with length greater than three, but there are two palindromic substrings with length three, namely, "aca" and "ada".

Sample Solution:-

C# Sharp Code:

``````using System;
using System.Collections.Generic;

namespace exercises
{
class Program
{
static void Main(string[] args)
{
// Initialize a string variable and display the original string
String str1;
str1 = "aaaaaabbbbccc";
Console.WriteLine("Original String: " + str1);

// Display the length of the longest substring without repeating characters
Console.WriteLine("Length of the longest substring without repeating characters of the said string:");
Console.WriteLine(longest_Palindrome(str1));

// Repeat the above steps for different strings
str1 = "BDEFGAABEF";
Console.WriteLine("Original String: " + str1);
Console.WriteLine("Length of the longest substring without repeating characters of the said string:");
Console.WriteLine(longest_Palindrome(str1));

str1 = "Python";
Console.WriteLine("Original String: " + str1);
Console.WriteLine("Length of the longest substring without repeating characters of the said string:");
Console.WriteLine(longest_Palindrome(str1));

str1 = "Java";
Console.WriteLine("Original String: " + str1);
Console.WriteLine("Length of the longest substring without repeating characters of the said string:");
Console.WriteLine(longest_Palindrome(str1));
}

// Method to find the length of the longest substring without repeating characters
public static string longest_Palindrome(string s)
{
// Convert the input string to a character array
var chars_array = s.ToCharArray();

// Initialize a boolean array to track palindrome substrings
var bool_arr = new bool[chars_array.Length, chars_array.Length];
int longest_start = 0;
int max_length = 1;

// Initialize the boolean array for single characters
for (int i = 0; i < chars_array.Length; i++)
{
bool_arr[i, i] = true;
}

// Check for palindrome substrings of length 2
for (int i = 0; i < chars_array.Length - 1; i++)
{
if (chars_array[i] == chars_array[i + 1])
{
bool_arr[i, i + 1] = true;
longest_start = i;
max_length = 2;
}
}

// Check for palindrome substrings of length greater than 2
for (int length = 3; length <= chars_array.Length; length++)
{
for (int i = 0; i < chars_array.Length - length + 1; i++)
{
int j = i + length - 1;
if (chars_array[i] == chars_array[j] && bool_arr[i + 1, j - 1])
{
bool_arr[i, j] = true;
if (max_length < (j - i))
{
max_length = j - i;
longest_start = i;
}
}
}
}

// Return the substring with the longest length without repeating characters
return s.Substring(longest_start, max_length);
}
}
}
```
```

Sample Output:

```Original String: aaaaaabbbbccc
Length of the longest substring without repeating characters of the said string:
aaaaa
Original String: BDEFGAABEF
Length of the longest substring without repeating characters of the said string:
AA
Original String: Python
Length of the longest substring without repeating characters of the said string:
P
Original String: Java
Length of the longest substring without repeating characters of the said string:
av
```

Flowchart :

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