9. Palindrome Number

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

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.

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

function isPalindrome(checkNumber: number): boolean {
    if (checkNumber < 0) {
        // 负数都会有「- 负数符号」，所以都没办法变成 Palindrome 整数
        return false;
    }

    // 取得计算左侧数字 divider 分母
    let divider = 1;
    while (checkNumber >= divider * 10) {
        // 假如分母 * 10 还是小于原本数字，表示分母还可以继续加
        divider *= 10;
    }


    while (checkNumber) {
        // 右侧数字
        let rightDigit = checkNumber % 10;
        // 左侧数字
        let leftDigit = Math.floor(checkNumber / divider);

        if (leftDigit != rightDigit) {
            // 假如数字不相同，表示这个不是 Palindrome 整数
            return false;
        }

        // 取得下一个要检查的整数，去除原数字的左右数字
        // 取馀数：去除最左边数字
        checkNumber = checkNumber % divider;
        // 除以 10：去除最右边数字
        checkNumber = Math.floor(checkNumber / 10);
        // 取得去除左右数字后，下一个检查的分母
        divider = divider / 100;
    }

    return true;
};