Longest Non-palindromic substring - GeeksforGeeks

23 Mar, 2021
Given a string of size n. The task is to find the length of the largest substring which is not 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 length of the longest non-palindromic substring.An efficient solution is based on 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' 
 
C++
Java
Python 3
C#
PHP
Javascript
// 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 notbool 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 palindromeint 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 aboveint main(){    string str = "abba";    cout << "Maximum length = "         << maxLengthNonPalinSubstring(str);    return 0;}
//Java implementation to find maximum length//substring which is not palindromepublic 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 implementation to find maximum# length substring which is not palindrome # utility function to check whether# a string is palindrome or notdef 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 palindromedef 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 Codeif __name__ == "__main__":         str = "abba"    print("Maximum length =",           maxLengthNonPalinSubstring(str)) # This code is contributed by ita_c
// C# implementation to find maximum length// substring which is not palindromeusing 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 implementation to find maximum length// substring which is not palindrome // utility function to check whether// a string is palindrome or notfunction isPalindrome($str){    $n = strlen($str);     // Check for palindrome.    for ($i = 0; $i < $n / 2; $i++)        if ($str[$i] != $str[$n - $i - 1])            return false;     // palindrome string    return true;} // function to find maximum length// substring which is not palindromefunction maxLengthNonPalinSubstring($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?>
<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)This article is contributed by Ayush Jauhari. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. 
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