9. Palindrome Number

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

Example 1:

Input: 121
Output: true

Example 2:

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

Follow up:

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

Runtime: 252 ms, faster than 51.01% of JavaScript online submissions for Palindrome Number.

/**
 * @param {number} x
 * @return {boolean}
 */
var isPalindrome = function(x) {
    if (x < 0) {
        return false;
    }
    x = x.toString();
    const mid = x.length / 2;
    let left, right;
    if (mid === ~~mid) {
        left = mid - 1;
        right = mid;
    } else {
        left = ~~mid;
        right = ~~mid;
    }
    const leftString = x.substring(0, left + 1);
    const rightString = x.substring(right, x.length);
    return leftString === rightString.split('').reverse().join('');
};

Runtime: 224 ms, faster than 99.51% of JavaScript online submissions for Palindrome Number.

/**
 * @param {number} x
 * @return {boolean}
 */
var isPalindrome = function(x) {
    if (x < 0) {
        return false;
    }
    const result = [];
    while(x) {
        result.push(x % 10);
        x = ~~(x / 10);
    }
    let i = 0;
    let j = result.length - 1;
    while(i < j) {
        if (result[i] !== result[j]) {
            return false;
        }
        i++;
        j--;
    }
    return true;
};