[LeetCode] 9. Palindrome Number

原题链接：https://leetcode.com/problems/palindrome-number/

1. 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?

2. Solution

My solution is as same as the LeetCode’s official solution. And it explains more detailed than me.
You can visit https://leetcode.com/problems/palindrome-number/solution/ for more details.

First of all, if x < 0 , it can not be a palindrome at all. We return false in this situation.

Then, if x’s digit in ones is 0, we need to return false, too.

Finally, we can use % and / to get x’s reverted number y. Just comparing with x and y is ok.
code

class Solution {
    public boolean isPalindrome(int x) {
        if(x <0){
            return false;
        }
        if(x%10 == 0 && x!=0){
            return false;
        }
        
        int y = 0;
        while(x > y){
            y = y*10 + x%10;
            x /= 10;
        }
        
        return ( x == y )||(x == y/10) ;
    }
}

3. Reference

https://leetcode.com/problems/palindrome-number/solution/