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PalindromeNumber.java
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PalindromeNumber.java
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package algorithm.topics.math;
/**
* Determine whether an integer is a palindrome. Do this without extra space.
* <p>
* Reference: <a href="https://leetcode.cn/problems/palindrome-number/">Palindrome Number</a>
* Difficulty: Easy
*
* @author hufeng
* @version PalindromeNumber.java, v 0.1 07/12/2017 12:51 AM Exp $
*/
public class PalindromeNumber {
/**
* Revert half of the number
*
* @param x
* @return
*/
public boolean isPalindrome(int x) {
// Special cases:
// As discussed above, when x < 0, x is not a palindrome.
// Also if the last digit of the number is 0, in order to be a palindrome,
// the first digit of the number also needs to be 0.
// Only 0 satisfy this property.
if (x < 0 || (x % 10 == 0 && x != 0)) {
return false;
}
int revertedNumber = 0;
while (x > revertedNumber) {
revertedNumber = revertedNumber * 10 + x % 10;
x /= 10;
}
// When the length is an odd number, we can get rid of the middle digit by revertedNumber/10
// For example when the input is 12321, at the end of the while loop we get x = 12, revertedNumber = 123,
// since the middle digit doesn't matter in palidrome(it will always equal to itself), we can simply get rid of it.
return x == revertedNumber || x == revertedNumber / 10;
}
}