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JavaScript Program to Check for Palindrome String using Recursion

Last Updated : 08 Jul, 2024
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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:

  • If there is only one character in the string, return true.
  • Else compare the first and last characters and recuring for the remaining substring.

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:

  • In this approach, we will check while traversing whether the ith and n-i-1th index are equal or not.
  • If there are not equal return false and if they are equal then continue with the recursion calls.

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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JavaScript Program for Sum of Digits of a Number using Recursion

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