9. Palindrome Number #

题目 #

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 a palindrome while 123 is not.

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:

-2^31 <= x <= 2^31 - 1

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

代码 #

const P10: &[i32] = &[1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000];

impl Solution {
    pub fn is_palindrome(x: i32) -> bool {
        if x < 0 { 
            return false;
        }
        if x == 0 {
            return true;
        }

        let mut divide = P10[(x as f64).log10().floor() as usize];

        let mut n = x;
        while n > 0 {
            let h = n / divide;
            let e = n % 10;

            if h != e {
                return false
            }

            n = n % divide / 10;
            divide = divide / 100;
        }

        return true;
    }
}