9. Palindrome Number

Given an integer x, return true if x is a palindrome, and false otherwise.

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

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

class Solution {
public:
    bool isPalindrome(int x) {
        if ((x < 0) || ((x % 10 == 0) && (x != 0))) return false;

        string s = to_string(x);
        int n = s.size();
        for (int i = 0; i < n / 2; i++) {
            if (s[i] != s[n - i - 1]) {
                return false;   // ❌ chỉ cần 1 cặp sai là không phải palindrome
            }
        }
        return true;  // ✅ chỉ return true khi duyệt hết mà không sai cặp nào
    }
};