Question

How to check if a number is palindrome recursively in JavaScript

Answer 1

function recursivelyCheckPalindrome(n) {
    if (n < 0) {
        return false; 
    }

    // This initializes a static variable inverse_number the first time the function is called. 
    // The use of typeof ensures this initialization only happens once.
    if (typeof recursivelyCheckPalindrome.inverse_number == 'undefined') {
        recursivelyCheckPalindrome.inverse_number = 0;
    }
      
    if (n == 0) {
        return false;
    }
    
    recursivelyCheckPalindrome.inverse_number = (recursivelyCheckPalindrome.inverse_number * 10) + (n % 10);
    recursivelyCheckPalindrome(parseInt(n / 10));
   
    return n === recursivelyCheckPalindrome.inverse_number;
}

const n = 12321;

if (recursivelyCheckPalindrome(n) === true) {
    console.log("Palindrome");
} else {
    console.log("NOT Palindrome");
}



/*
run:
  
Palindrome
           
*/

 

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Answer 2

function recursivelyCheckPalindrome(n, original) {
    if (n === 0) {
        const originalStr = Math.abs(original).toString();
        
        return originalStr === originalStr.split('').reverse().join('');
    }
 
    return recursivelyCheckPalindrome(Math.floor(n / 10), original);
}
 
const n = 73137;
 
if (recursivelyCheckPalindrome(n, n)) {
    console.log("Palindrome");
} else {
    console.log("NOT Palindrome");
}



/*
run:
  
Palindrome
           
*/

 

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