Palindrome Check in JavaScript

1// Palindrome: reads same forwards and backwards
2// Examples: 121, "madam", "racecar"
3
4// Method 1: String palindrome
5function isPalindromeString(str) {
6    str = str.toLowerCase().replace(/[^a-z0-9]/g, '');
7    let reversed = str.split('').reverse().join('');
8    return str === reversed;
9}
10
11console.log("madam:", isPalindromeString("madam"));
12console.log("hello:", isPalindromeString("hello"));
13console.log("A man a plan a canal Panama:", isPalindromeString("A man a plan a canal Panama"));
14
15// Method 2: Number palindrome
16function isPalindromeNumber(num) {
17    let original = num;
18    let reversed = 0;
19    
20    while (num > 0) {
21        reversed = reversed * 10 + (num % 10);
22        num = Math.floor(num / 10);
23    }
24    
25    return original === reversed;
26}
27
28console.log("\nNumber palindrome:");
29console.log("121:", isPalindromeNumber(121));
30console.log("123:", isPalindromeNumber(123));
31console.log("1221:", isPalindromeNumber(1221));
32
33// Method 3: Two-pointer approach (efficient)
34function isPalindromeTwoPointer(str) {
35    str = str.toLowerCase().replace(/[^a-z0-9]/g, '');
36    let left = 0;
37    let right = str.length - 1;
38    
39    while (left < right) {
40        if (str[left] !== str[right]) {
41            return false;
42        }
43        left++;
44        right--;
45    }
46    return true;
47}
48
49console.log("\nTwo-pointer approach:");
50console.log("racecar:", isPalindromeTwoPointer("racecar"));
51console.log("hello:", isPalindromeTwoPointer("hello"));
52
53// Method 4: Recursive approach
54function isPalindromeRecursive(str) {
55    str = str.toLowerCase().replace(/[^a-z0-9]/g, '');
56    
57    if (str.length <= 1) return true;
58    if (str[0] !== str[str.length - 1]) return false;
59    
60    return isPalindromeRecursive(str.slice(1, -1));
61}
62
63console.log("\nRecursive approach:");
64console.log("level:", isPalindromeRecursive("level"));
65console.log("world:", isPalindromeRecursive("world"));