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: Could you solve it without converting the integer to a string?
Difficulty:Easy
Category:Math
Analyze
验证回文数字, 直接对整数进行操作,我们可以利用取整和取余来获得我们想要的数字, 每计算一次, 去掉收尾各一个数字, 循环计算.
Solution
class Solution {
public:
bool isPalindrome(int x) {
if (x < 0) return false;
int div = 1;
while (x / div >= 10) div *= 10;
while (x > 0) {
int left = x / div;
int right = x % 10;
if (left != right) return false;
x = (x % div) / 10;
div /= 100;
}
return true;
}
};
Solution 2
class Solution {
public:
bool isPalindrome(int x) {
if (x < 0 || (x % 10 == 0 && x != 0)) return false;
int revertNum = 0;
int cal_data = x;
while (cal_data != 0) {
revertNum = revertNum * 10 + cal_data % 10;
cal_data /= 10;
}
return (revertNum == x) ? true : false;
}
};