Recursive function to check if a string is palindrome

2.6

Given a string, write a recursive function that check if the given string is palindrome, else not palindrome.

Examples:

Input : malayalam
Output : Yes
Reverse of malayalam is also
malayalam.

Input : max
Output : No
Reverse of max is not max.

We have discussed an iterative function here.

The idea of recursive function is simple :

1) If there is only one character in string
   return true.
2) Else compare first and last characters
   and recur for remaining substring.

Below is the implementation of above steps.

C

// A recursive C program to check whether
// a given number is palindrome or not
#include <stdio.h>
#include <string.h>
#include <stdbool.h>

// A recursive function that check a str[s..e]
// is palindrome or not.
bool isPalRec(char str[], int s, int e)
{
    // If there is only one character
    if (s == e)
       return true;

    // If first and last characters do not match
    if (str[s] != str[e])
       return false;

    // If there are more than two characters,
    // check if middle substring is also
    // palindrome or not.
    if (s < e+1)
       return isPalRec(str, s+1, e-1);

    return true;
}

bool isPalindrome(char str[])
{
   int n = strlen(str);

   // An empty string is considered as
   // palindrome
   if (n == 0)
     return true;

   return isPalRec(str, 0, n-1);
}

// Main Function
int main()
{
    char str[] = "geeg";

    if (isPalindrome(str))
       printf("Yes");
    else
       printf("No");

    return 0;
}

Java

// A recursive JAVA program to check whether
// a given String is palindrome or not
import java.io.*;

class GFG
{
    // A recursive function that check a str(s..e)
    // is palindrome or not.
    static boolean isPalRec(String str, int s, int e)
    {
        // If there is only one character
        if (s == e)
            return true;

        // If first and last characters do not match
        if ((str.charAt(s)) != (str.charAt(e)))
            return false;

        // If there are more than two characters,
        // check if middle substring is also
        // palindrome or not.
        if (s < e+1)
            return isPalRec(str, s+1, e-1);

        return true;
    }

    static boolean isPalindrome(String str)
    {
        int n = str.length();

    // An empty string is considered as
    // palindrome
        if (n == 0)
            return true;

        return isPalRec(str, 0, n-1);
    }

    // Main Function
    public static void main(String args[])
    {
        String str = "geeg";

        if (isPalindrome(str))
            System.out.println("Yes");
        else
            System.out.println("No");
    }
}

// This code is contributed by Nikita Tiwari

Python

# A recursive Python program to check whether
# a given number is palindrome or not

# A recursive function that check a str[s..e]
# is palindrome or not.
def isPalRec(st, s, e) :
    
    # If there is only one character
    if (s == e):
        return True

    # If first and last characters do not match
    if (st[s] != st[e]) :
        return False

    # If there are more than two characters,
    # check if middle substring is also
    # palindrome or not.
    if (s < e+1) :
        return isPalRec(st, s+1, e-1);

    return True

def isPalindrome(st) :
    n = len(st)
    
    # An empty string is considered as
    # palindrome
    if (n == 0) :
        return True
    
    return isPalRec(st, 0, n-1);


# Main Function
st = "geeg"
if (isPalindrome(st)) :
    print "Yes"
else :
    print "No"
    
# This code is contributed by Nikita Tiwari.


Output:

Yes

This article is contributed by Sahil Rajput. 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.

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