Palindrome Number
(#9), Easy
Category: Math
Problem Statement
Given an integer `x`, return `true` if `x` is a palindrome, and `false` otherwise. A palindrome is a number that reads the same backward as forward. Negative numbers are **not** considered palindromes.
Examples
Input: x = 121
Output: true
Explanation: 121 reads the same forward and backward.
Input: x = -121
Output: false
Explanation: Reversed = 121-, which is not valid.
Input: x = 10
Output: false
Explanation: Reversed = 01, which is not equal to 10.
Approach
Approach: Reverse Integer Comparison
- If `x` is negative, immediately return `false`.
- Initialize a `reversed` variable to 0 and store the original value in a temporary variable `temp`.
- While `temp > 0`:
- - Extract the last digit: `lastDigit = temp % 10`
- - Build reversed number: `reversed = reversed * 10 + lastDigit`
- - Remove last digit: `temp = Math.floor(temp / 10)`
- After the loop, compare `reversed` with `x`. If equal, return `true`; otherwise, return `false`.
// 🔹 Approach: Reversing Number
var isPalindrome = function (x) {
if (x < 0) return false;
let temp = x;
let reversed = 0;
while (temp > 0) {
let lastDigit = temp % 10;
reversed = reversed * 10 + lastDigit;
temp = Math.floor(temp / 10);
}
return reversed === x;
};Complexity
Time: O(log₁₀n) – We divide the number by 10 each iteration
Space: O(1) – Constant space for variables