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Palindrome Number

Problem​

Given an integer x, return true if x is palindrome integer.

An integer is a palindrome when it reads the same backward as forward.

  • For example, 121 is a palindrome while 123 is not.

 

Example 1:

Input: x = 121
Output: true
Explanation: 121 reads as 121 from left to right and from right to left.

Example 2:

Input: x = -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: x = 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

 

Constraints:

  • -231 <= x <= 231 - 1

Solution​

/**
 * @param {number} x
 * @return {boolean}
 */
var isPalindrome = function(x) {
    return x === parseInt(x.toString().split("").reverse().join(""));
};

We convert x to a string, reverse it, convert it back to an integer, and check if it still equals x .

Follow-up​

Could you solve it without converting the integer to a string?

Solution​

/**
 * @param {number} x
 * @return {boolean}
 */
var isPalindrome = function(x) {
    if (x < 0) {
        return false;
    }
    let y = x;
    let reverse = 0;
    while (y !== 0) {
        reverse *= 10;
        reverse += y % 10;
        y = Math.floor(y / 10);
    }
    return reverse === x;
};

We reverse x using division and check if the reverse still equals x.