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Longest Non-palindromic substring

Last Updated : 11 Jul, 2022
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Given a string of size n. The task is to find the length of the largest substring which is not a palindrome.

Examples: 

Input : abba 
Output : 3
Here maximum length non-palindromic substring is
'abb' which is of length '3'. There could be other
non-palindromic sub-strings also of length three 
like 'bba' in this case.

Input : a
Output : 0

A simple solution is to consider every substring and check if it is palindrome or not. Finally, return the length of the longest non-palindromic substring.

An efficient solution is based on the below approach. 

Check for the case where all characters of
the string are same or not.
    If yes, then answer will be '0'.
Else check whether the given string of size 
'n' is palindrome or not. 
    If yes, then answer will be 'n-1'
Else answer will be 'n'

Implementation:

C++ 
// C++ implementation to find maximum length
// substring which is not palindrome
#include <bits/stdc++.h>
using namespace std;

// utility function to check whether
// a string is palindrome or not
bool isPalindrome(string str)
{
    // Check for palindrome.
    int n = str.size();
    for (int i=0; i < n/2; i++)
        if (str.at(i) != str.at(n-i-1))
            return false;

    // palindrome string
    return true;
}

// function to find maximum length
// substring which is not palindrome
int maxLengthNonPalinSubstring(string str)
{
    int n = str.size();
    char ch = str.at(0);

    // to check whether all characters
    // of the string are same or not
    int i = 1;
    for (i=1; i<n; i++)
        if (str.at(i) != ch)
            break;

    // All characters are same, we can't
    // make a non-palindromic string.
    if (i == n)
        return 0;

    // If string is palindrome, we can make
    // it non-palindrome by removing any
    // corner character
    if (isPalindrome(str))
        return n-1;

    // Complete string is not a palindrome.
    return n;
}

// Driver program to test above
int main()
{
    string str = "abba";
    cout << "Maximum length = "
         << maxLengthNonPalinSubstring(str);
    return 0;
}
Java 
//Java implementation to find maximum length
//substring which is not palindrome
public class GFG
{
    // utility function to check whether
    // a string is palindrome or not
    static Boolean isPalindrome(String str)
    {
        int n = str.length();

        // Check for palindrome.
        for (int i = 0; i < n/2; i++)
            if (str.charAt(i) != str.charAt(n-i-1))
                return false;

        // palindrome string
        return true;
    }

    // function to find maximum length
    // substring which is not palindrome
    static int maxLengthNonPalinSubstring(String str)
    {
        int n = str.length();
        char ch = str.charAt(0);

        // to check whether all characters
        // of the string are same or not
        int i = 1;
        for (i = 1; i < n; i++)
            if(str.charAt(i) != ch)
                break;

        // All characters are same, we can't
        // make a non-palindromic string.
        if (i == n)
            return 0;

        // If string is palindrome, we can make
        // it non-palindrome by removing any
        // corner character
        if (isPalindrome(str))
            return n-1;

        // Complete string is not a palindrome.
        return n;
    }

    // Driver Program to test above function
    public static void main(String args[])
    {
        String str = "abba";
        System.out.println("Maximum Length = "
             + maxLengthNonPalinSubstring(str));
    }
}
// This code is contributed by Sumit Ghosh
Python 3 
# Python 3 implementation to find maximum 
# length substring which is not palindrome

# utility function to check whether
# a string is palindrome or not
def isPalindrome(str):
    
    # Check for palindrome.
    n = len(str)
    for i in range(n // 2):
        if (str[i] != str[n - i - 1]):
            return False

    # palindrome string
    return True

# function to find maximum length
# substring which is not palindrome
def maxLengthNonPalinSubstring(str):
    n = len(str)
    ch = str[0]

    # to check whether all characters
    # of the string are same or not
    i = 1
    for i in range(1, n):
        if (str[i] != ch):
            break

    # All characters are same, we can't
    # make a non-palindromic string.
    if (i == n):
        return 0

    # If string is palindrome, we can make
    # it non-palindrome by removing any
    # corner character
    if (isPalindrome(str)):
        return n - 1

    # Complete string is not a palindrome.
    return n

# Driver Code
if __name__ == "__main__":
    
    str = "abba"
    print("Maximum length =", 
           maxLengthNonPalinSubstring(str))

# This code is contributed by ita_c
C# 
// C# implementation to find maximum length
// substring which is not palindrome
using System;

class GFG {
    
    // utility function to check whether
    // a string is palindrome or not
    static bool isPalindrome(String str)
    {
        int n = str.Length;

        // Check for palindrome.
        for (int i = 0; i < n / 2; i++)
            if (str[i] != str[n - i - 1])
                return false;

        // palindrome string
        return true;
    }

    // function to find maximum length
    // substring which is not palindrome
    static int maxLengthNonPalinSubstring(String str)
    {
        int n = str.Length;
        char ch = str[0];

        // to check whether all characters
        // of the string are same or not
        int i = 1;
        for (i = 1; i < n; i++)
            if(str[i] != ch)
                break;

        // All characters are same, we can't
        // make a non-palindromic string.
        if (i == n)
            return 0;

        // If string is palindrome, we can 
        // make it non-palindrome by removing 
        // any corner character
        if (isPalindrome(str))
            return n-1;

        // Complete string is not a palindrome.
        return n;
    }

    // Driver code
    public static void Main()
    {
        String str = "abba";
        Console.Write("Maximum Length = "
                      + maxLengthNonPalinSubstring(str));
    }
}

// This code is contributed by nitin mittal
PHP 
<?php
// PHP implementation to find maximum length
// substring which is not palindrome

// utility function to check whether
// a string is palindrome or not
function isPalindrome($str)
{
    $n = strlen($str);

    // Check for palindrome.
    for ($i = 0; $i < $n / 2; $i++)
        if ($str[$i] != $str[$n - $i - 1])
            return false;

    // palindrome string
    return true;
}

// function to find maximum length
// substring which is not palindrome
function maxLengthNonPalinSubstring($str)
{
    $n = strlen($str);
    $ch = $str[0];

    // to check whether all characters
    // of the string are same or not
    $i = 1;
    for ($i = 1; $i < $n; $i++)
        if($str[$i] != $ch)
            break;

    // All characters are same, we can't
    // make a non-palindromic string.
    if ($i == $n)
        return 0;

    // If string is palindrome, we can 
    // make it non-palindrome by removing 
    // any corner character
    if (isPalindrome($str))
        return ($n - 1);

    // Complete string is not a palindrome.
    return $n;
}

// Driver code
$str = "abba";
echo "Maximum Length = ",
      maxLengthNonPalinSubstring($str);

// This code is contributed by ajit
?>
JavaScript 
<script>

//Javascript implementation to find maximum length 
//substring which is not palindrome 
    
    // utility function to check whether 
    // a string is palindrome or not 
    function isPalindrome(str)
    {
        let n=str.length;
        // Check for palindrome. 
        for (let i = 0; i < n/2; i++) 
        {
            if(str[i] != str[n-i-1])
                return false;
        }
        // palindrome string 
        return true;
    }
    // function to find maximum length 
    // substring which is not palindrome
    function maxLengthNonPalinSubstring(str)
    {
        let n = str.length;
        let ch=str[0];
        // to check whether all characters 
        // of the string are same or not
        let i = 1; 
        for (i = 1; i < n; i++)
        {
            if(str[i] != ch)
            {
                break;
            }
        }
        // All characters are same, we can't 
        // make a non-palindromic string. 
        if (i == n) 
            return 0; 
        
        // If string is palindrome, we can make 
        // it non-palindrome by removing any 
        // corner character 
        if (isPalindrome(str))
            return n-1; 
        
        // Complete string is not a palindrome. 
        return n; 
    }
    // Driver Program to test above function 
    let str = "abba"; 
    document.write("Maximum Length = " + maxLengthNonPalinSubstring(str)); 
    
    // This code is contributed by avanitrachhadiya2155
    
</script>

Output
Maximum length = 3

Time Complexity: O(n)
Auxiliary Space: O(n)

 


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Longest Non-palindromic substring

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Ayush Jauhari
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