9.PalindromeNumber.md

9. Palindrome Number

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward. Follow up: Could you solve it without converting the integer to a string?

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

Solution

• java

/*
  Success Details:
  Runtime: 6 ms, faster than 99.97% of Java online submissions for Palindrome Number.
  Memory Usage: 38.1 MB, less than 88.20% of Java online submissions for Palindrome Number.      
 */
class Solution {
    public boolean isPalindrome(int x) {
        if (x < 0 || (x != 0 && x % 10 == 0)) {
            return false;
        }
        int num = 0;
        while (num < x) {
            num = num * 10 + x % 10;
            x /= 10;
        }
        return num == x || x == num / 10;
    }
}