题目

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

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Example1

Input: 121
Output: true

Example1

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.

Example3

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?

题目大意

判断一个整数是否是回文数。回文数是指正序(从左向右)和倒序(从右向左)读都是一样的整数。

解题思路

判断一个整数是不是回文数。
很简答，要注意负数，个位数，10都不是回文数。其他的整数再按照回文的规则判断。

代码

package leetcode;

public class D09_PalindromeNumber {

    public static boolean isPalindrome(int x) {
        int x1 = x;
        int tmp = 0;
        if (x1 < 0) return false;
        while (x != 0) {
            tmp = tmp * 10 + x % 10;
            x /= 10;
        }
        if (tmp == x1) {
            return true;
        } else {
            return false;
        }
    }

}

复杂度分析

* 时间复杂度：O(log(N)),x中大约有log10(x)位数字。
* 空间复杂度：O(1)。