PalindromeNumber.java

/**
 * Determine whether an integer is a palindrome. Do this without extra space.
 *
 * <p>Some hints: Could negative integers be palindromes? (ie, -1)
 *
 * <p>If you are thinking of converting the integer to string, note the restriction of using extra
 * space.
 *
 * <p>You could also try reversing an integer. However, if you have solved the problem "Reverse
 * Integer", you know that the reversed integer might overflow. How would you handle such case?
 *
 * <p>There is a more generic way of solving this problem.
 */
public class PalindromeNumber {
  public boolean isPalindrome(int x) {
    if (x < 0) return false;
    int k = 1;
    while (x / k >= 10) {
      k *= 10;
    }
    while (x >= 10) {
      int left = x / k;
      int right = x - x / 10 * 10;
      if (left != right) return false;
      x = (x - x / k * k) / 10;
      k /= 100;
    }
    return true;
  }
}