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;
}
}
}