Description
https://leetcode.com/problems/palindrome-number/
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?
Explanation
Negative numbers are not palindrome numbers, e.g., -121. We can exclude negative numbers first.
Then by comparing the integer number and its reversed integer, we can determine whether the integer is a palindrome.
Java Solution
public class Solution {
public boolean isPalindrome(int x) {
if (x < 0 || x != 0 && x % 10 == 0) {
return false;
}
// reverse process
int reversed = 0;
int original = x;
while (x != 0) {
reversed = reversed * 10 + x % 10;
x = x / 10;
}
return reversed == original;
}
}
Python Solution
class Solution:
def isPalindrome(self, x: int) -> bool:
if x < 0:
return False
reverse = 0
original = x
while x > 0:
reverse = reverse * 10 + x % 10
x = x // 10
return reverse == original- Time complexity: O(N)
- Space complexity: O(1)