Palindrome Number

Solved

Difficulty: Basic Accuracy: — Submissions: 0 Points: 1

Given an integer n, return true if it reads the same forwards and backwards, and false otherwise. Negative numbers are not palindromes because of the leading minus sign.

Examples:

Input: n = 12321

Output: true

Explanation: Reversed, 12321 is still 12321.

Input: n = -121

Output: false

Explanation: Reversed it would be 121-, which is not the same.

Input: n = 10

Output: false

Explanation: Reversed it is 01.

Constraints:

-10^18 ≤ n ≤ 10^18

Expected Complexities

Time Complexity: O(log n) Auxiliary Space: O(1)

Company Tags

Adobe Paytm

Topic Tags

Basic Math

Build the reversed number digit by digit: peel off the last digit with n % 10 and append it to the reverse with reverse * 10 + digit. Compare at the end. Rejecting negatives up front keeps the loop simple.

class Solution {
    public boolean isPalindrome(long n) {
        if (n < 0) return false;
        long original = n, reversed = 0;
        while (n > 0) {
            reversed = reversed * 10 + n % 10;
            n /= 10;
        }
        return original == reversed;
    }
}