Integers: Check palindrome

Problem statements:

• Given an integer x, return true if x is a palindrome, and false otherwise.

  • Example 1:

    • Input: x = 121
    • Output: true
    • Explanation: 121 reads as 121 from left to right and from right to left.

  • Example 2:

    • Input: x = -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: x = 10
  • Output: false
  • Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

• Constraints:

  • -231 <= x <= 231 - 1

• Follow up:

  • Could you solve it without converting the integer to a string?

Soltuions:

1. Slice num while adding digits to reverse

• Approach:
  • Inital check:
    • False: if n < 0
    • False: if x != 0 && x % 10 == 0
  • Add last digit to rev and slice it from n.
    • Do it till n is greater than rev.
  • Check palindrome:
    • True: if rev is equal to n.
    • True: if rev / 10 is equal to n (for inputs with odd digit count).
    • Otherwise false.

      public boolean isPalindrome(int x) {

          // if x < 0
          if(x < 0) return false;
          if(x != 0 && x % 10 == 0) return false;

          int reverse = 0;
          // Loop till rev is smaller than num
          while(x > reverse) {
              int ld = x % 10;
              reverse = (reverse * 10) + ld;
              x = x / 10;
          }
          
          
          if(reverse == x) {
            // When n has odd numers of digits
            return true;
          } else if(x == (reverse / 10)) {
            // When n has odd numers of digits
            return true;
          } else {
              return false;
          }
      }