Palindrome Number Explained

Problem Statement

Given an integer x, determine if it is a palindrome. An integer is a palindrome when it reads the same forwards and backwards. For example, 121 is a palindrome, but 123 is not. This problem tests your ability to manipulate numbers without converting them to strings for an efficient solution.

Example

Input: x = 121

Output: true

Explanation: 121 reads the same forwards and backwards.

Code

public class Solution {
    public boolean isPalindrome(int x) {
        if (x < 0) return false;
        int reversed = 0, original = x;
        while (x > 0) {
            int digit = x % 10;
            if (reversed > Integer.MAX_VALUE / 10) return false;
            reversed = reversed * 10 + digit;
            x /= 10;
        }
        return reversed == original;
    }

    public static void main(String[] args) {
        Solution sol = new Solution();
        System.out.println(sol.isPalindrome(121)); // true
    }
}
            

def is_palindrome(x):
    if x < 0:
        return False
    reversed_num = 0
    original = x
    while x > 0:
        digit = x % 10
        reversed_num = reversed_num * 10 + digit
        x //= 10
    return reversed_num == original

# Example usage
print(is_palindrome(121))  # True
            

function isPalindrome(x) {
    if (x < 0) return false;
    let reversed = 0, original = x;
    while (x > 0) {
        let digit = x % 10;
        if (reversed > Math.floor(Number.MAX_SAFE_INTEGER / 10)) return false;
        reversed = reversed * 10 + digit;
        x = Math.floor(x / 10);
    }
    return reversed === original;
}

// Example usage
console.log(isPalindrome(121)); // true
            

Explanation

• If the number is negative, it’s not a palindrome (e.g., -121).
• Reverse the number by extracting digits using modulo and building the reversed number.
• Check for overflow in languages like Java and JavaScript to avoid incorrect results.
• Compare the reversed number with the original.
• Return true if they match, false otherwise.

Note