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?

bool isPalindrome(int x) { // time: O(logx); space: O(1)
    if (x < 0) return false;
    int orig = x;
    long num = 0;
    while (x) {
        num = num * 10 + x % 10;
        x /= 10;
    }
    return orig == num;
}