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Recursive function to check if a string is palindrome

  • Difficulty Level : Easy
  • Last Updated : 28 Jun, 2021

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

Examples: 

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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 a 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 the above idea: 

C++




// A recursive C++ program to
// check whether a given number
// is palindrome or not
#include <bits/stdc++.h>
using namespace std;
 
// 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))
    cout << "Yes";
    else
    cout << "No";
 
    return 0;
}
 
// This code is contributed by shivanisinghss2110

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);
}
 
// Driver Code
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);
    }
 
    // 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

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

C#




// 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.

PHP




<?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.
?>

Javascript




<script>
    // A recursive javascript program to
    // check whether a given String
    // 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.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;
    }
 
    function isPalindrome( str) {
        var n = str.length;
 
        // An empty string is
        // considered as palindrome
        if (n == 0)
            return true;
 
        return isPalRec(str, 0, n - 1);
    }
 
    // Driver Code
     
        var str = "geeg";
 
        if (isPalindrome(str))
            document.write("Yes");
        else
            document.write("No");
 
// This code contributed by gauravrajput1
</script>

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 write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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