Palindrome Number之Java实现

Posted 2021-11-29

一、题目

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?

二、解题思路

1、此题为判断一个数值是否是回文数，即将数值反转后是否等于原数值，如是，则为回文数；
2、先判断数值x是否小于0，如小于0则返回false；
3、再判断x是否等于0，如是，则返回true；
4、如上面两种情况都不符合，则将数值x循环取余取出每一位上的数存入集合中；
5、循环将集合中的数取出，求得反转后的数值；
6、与数值x比较是否相等，如是，则返回true，否则返回false。

三、代码实现

public boolean isPalindrome(int x) {
    if (x < 0) {
        return false;
    } else if (x == 0) {
        return true;
    } else {
        int temp = x;
        int result = 0;
        List<Integer> list = new ArrayList<Integer>();

        while (temp != 0) {
            list.add(temp % 10);
            temp = temp / 10;
        }

        for (int i = 0; i < list.size(); i++) {
            result = result + list.get(i) * (int)Math.pow(10, list.size() - 1 - i);
        }

        if (result == x) {
            return true;
        } else {
            return false;
        }
    }
}