JavaScript Program to Check for Palindrome String using Recursion (original) (raw)

Last Updated : 08 Jul, 2024

Given a string, write a recursive function that checks if the given string is a palindrome, else, not a palindrome. A string is called a palindrome if the reverse of the string is the same as the original one. For example - “madam”, “racecar”, etc.

**What is Recursion?

The process in which a function calls itself directly or indirectly is called recursion and the corresponding function is called a recursive function. In the recursive program, the solution to the base case is provided and the solution to the bigger problem is expressed in terms of smaller problems.

**Examples:

Input : NITIN Output : Yes Reverse of NITIN is also NITIN. Input : CAR Output : No Reverse of CAR is not CAR it is RAC

Approach 1:

**Example:

JavaScript `

// A recursive JavaScript program to // check whether a given String // is palindrome or not

function checkPalindrome(str, s, e) {

// If there is only one character
if (s == e)
    return true;

// If first and last characters
// does 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 checkPalindrome(str, s + 1, e - 1);

return true;

}

function isPalindrome(str) { let len = str.length;

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

return checkPalindrome(str, 0, len - 1);

}

// Driver Code

let str = "malayalam";

if (isPalindrome(str)) console.log("Yes, it is palindrome"); else console.log("No,it is not palindrome");

`

Output

Yes, it is palindrome

Approach 2:

**Example:

JavaScript `

function checkPalindrome(s, i) { if (i > s.length / 2) { return true; } return s[i] == s[s.length - i - 1] && checkPalindrome(s, i + 1) }

let str = "racecar"; let ans = checkPalindrome(str, 0); if (ans == true) { console.log("Yes,it is palindrome"); } else { console.log("No,it is not palindrome"); }

`

Output

Yes,it is palindrome

**Time Complexity: O(n)

**Auxiliary Space: O(n)

Approach 3: Using Substring Comparison

In this approach, we will use the substring method to compare the first and last characters, and recursively check the middle substring.

**Example: This example shows the implementation of the above-mentioned approach.

JavaScript `

function isPalindrome(str) { if (str.length <= 1) { return true; }

if (str[0] !== str[str.length - 1]) {
    return false;
}

return isPalindrome(str.substring(1, str.length - 1));

}

let str = "deified"; if (isPalindrome(str)) { console.log("Yes, it is palindrome"); } else { console.log("No, it is not palindrome"); }

`

Output

Yes, it is palindrome

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