Recursive function to check if a string is palindrome

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 idea :

C

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// 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);
}
  
// Driver Code
int main()
{
    char str[] = "geeg";
  
    if (isPalindrome(str))
    printf("Yes");
    else
    printf("No");
  
    return 0;
}

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Java

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// 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);
    }
  
    // Driver Code
    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

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Python

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

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C#

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// A recursive C# program to 
// check whether a given number
// is palindrome or not
using System;
  
class GFG
{
  
    // A recursive function that 
    // check a str(s..e)
    // is palindrome or not.
    static bool isPalRec(String str, 
                         int s, 
                         int e)
    {
          
        // If there is only one character
        if (s == e)
            return true;
  
        // If first and last character
        // 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;
    }
  
    static bool 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);
    }
  
    // Driver Code
    public static void Main()
    {
        String str = "geeg";
  
        if (isPalindrome(str))
            Console.Write("Yes");
        else
            Console.Write("No");
    }
}
  
// This code is contributed by Nitin Mittal.

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PHP

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<?php
// A recursive php program to 
// check whether a given number
// is palindrome or not
  
  
// A recursive function that 
// check a str[s..e] is 
// palindrome or not.
function isPalRec($str, $s,$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;
}
  
function isPalindrome($str)
{
$n = strlen($str);
  
// An empty string is 
// considered as palindrome
if ($n == 0)
    return true;
  
return isPalRec($str, 0, $n - 1);
}
  
// Driver Code
{
    $str = "geeg";
  
    if (isPalindrome($str))
    echo("Yes");
    else
    echo("No");
  
    return 0;
}
  
// This code is contributed 
// by nitin mittal.
?>

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Output :

Yes

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Improved By : nitin mittal



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