LeetCode 9. Palindrome Number

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 palindrome while 123 is not.

Example 1:

Input: x = 121
Output: true

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.

Example 4:

Input: x = -101
Output: false

Constraints:

• -231 <= x <= 231 - 1

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

Solution:

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class Solution {
public:
    bool isPalindrome(int x) {
        if (x == 0) return true;
        if (x < 0) return false;
        if (x % 10 == 0) return false;
        
        int sum = 0;
        while (x > sum) {
            sum = sum * 10 + x % 10;
            x /= 10;
        }
        return (x == sum) || (x == sum / 10);
    }
    
};