Palindrome Number

LeetCode Q 9 - Palindrome Number

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Solution

Solution 1: Transform the int to string

Code:

public boolean isPalindrome(int x) {
  if (x < 0) return false;
  
  String s = x + "";
  
  int i = 0, j = s.length() - 1;
  while (i < j) {
    if (s.charAt(i++) != s.charAt(j--))
      return false;
  }
  
  return true;
}

Solution 2: Revert half of the int

Second, we can revert the number itself, and then compare the number with original number, if they are the same, then the number is a palindrome. However, if the reversed number is larger than Integer.MAX_VALUE, we will hit integer overflow problem.
Following the thoughts , to avoid the overflow issue of the reverted number, what if we only revert half of the \text{int}int number? After all, the reverse of the last half of the palindrome should be the same as the first half of the number, if the number is a palindrome.

Code:

public boolean isPalindrome(int x) {
  if (x < 0 || (x % 10 == 0 && x != 0)) //30, 400,... are not palindrome
      return false;
  int num = 0;
  while (x > num) {
    num = 10 * num + x % 10;
    x /= 10;
  }
  
  return x == num || x == num / 10;
}