String Palindrome Check

Program to check if a string is palindrome

BeginnerTopic: String Programs

JavaScript String Palindrome Check Program

This program helps you to learn the fundamental structure and syntax of JavaScript programming.

// Method 1: Compare with reversed string
function isPalindrome1(str) {
    str = str.toLowerCase().replace(/[^a-z0-9]/g, '');
    return str === str.split('').reverse().join('');
}

console.log("madam:", isPalindrome1("madam"));
console.log("hello:", isPalindrome1("hello"));
console.log("A man a plan:", isPalindrome1("A man a plan a canal Panama"));

// Method 2: Two-pointer approach
function isPalindrome2(str) {
    str = str.toLowerCase().replace(/[^a-z0-9]/g, '');
    let left = 0;
    let right = str.length - 1;
    
    while (left < right) {
        if (str[left] !== str[right]) {
            return false;
        }
        left++;
        right--;
    }
    return true;
}

console.log("\nTwo-pointer:");
console.log("racecar:", isPalindrome2("racecar"));
console.log("world:", isPalindrome2("world"));

// Method 3: Recursive approach
function isPalindrome3(str) {
    str = str.toLowerCase().replace(/[^a-z0-9]/g, '');
    
    if (str.length <= 1) return true;
    if (str[0] !== str[str.length - 1]) return false;
    
    return isPalindrome3(str.slice(1, -1));
}

console.log("\nRecursive:");
console.log("level:", isPalindrome3("level"));
console.log("hello:", isPalindrome3("hello"));

// Method 4: Using every method
function isPalindrome4(str) {
    str = str.toLowerCase().replace(/[^a-z0-9]/g, '');
    return str.split('').every((char, i) => {
        return char === str[str.length - 1 - i];
    });
}

console.log("\nUsing every:");
console.log("deed:", isPalindrome4("deed"));

Output

madam: true
hello: false
A man a plan: true

Two-pointer:
racecar: true
world: false

Recursive:
level: true
hello: false

Using every:
deed: true

Understanding String Palindrome Check

This program demonstrates different methods to check if a string is a palindrome.

Palindrome Definition

Reads same forwards and backwards:

•"madam" → "madam" ✅

•"hello" → "olleh" ❌

Method 1: Compare with Reversed

Simple approach:

str === str.split('').reverse().join('');

String Cleaning:

•toLowerCase(): Case-insensitive

•replace(/[^a-z0-9]/g, ''): Remove non-alphanumeric

Method 2: Two-Pointer

Most efficient:

let left = 0;
let right = str.length - 1;
while (left < right) {
    if (str[left] !== str[right]) return false;
    left++;
    right--;
}

return true;

Pros:

•O(n) time, O(1) space

•No string reversal needed

•Most efficient

Method 3: Recursive

Elegant but less efficient:

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

return isPalindrome(str.slice(1, -1));

Method 4: Every Method

Functional approach:

str.split('').every((char, i) => {
});

    return char === str[str.length - 1 - i];

Every Method:

•Tests if all elements pass test

•Returns false on first failure

Time Complexity:

•All methods: O(n)

•Two-pointer: Best space efficiency

When to Use:

Reversed comparison

: Simplest

Two-pointer

: Most efficient

Recursive

: Learning recursion

Every

: Functional style

Let us now understand every line and the components of the above program.

Note: To write and run JavaScript programs, you need to set up the local environment on your computer. Refer to the complete article Setting up JavaScript Development Environment. If you do not want to set up the local environment on your computer, you can also use online IDE to write and run your JavaScript programs.

Anagram Check

Reverse a String