leetcode: 9. Palindrome Number

Difficulty

Easy

Description

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?

Solution

Time Complexity: O(log(x))
Space Complexity: O(1)

class Solution {
    public boolean isPalindrome(int x) {
        if (x < 0)
            return false;
        if (x == 0)
            return true;
        int rev = 0;
        int ori = x;
        while (x != 0) {     //翻转数字判断
            if (rev > Integer.MAX_VALUE/10 || (rev == Integer.MAX_VALUE/10 && x % 10 > 7))
                return false;
            rev = rev * 10 + x % 10;
            x /= 10;
        }
        return rev == ori ? true : false;       
    }
}