Is an Integer the Same Forwards and Backwards

easy math palindrome

Problem

Return true if the decimal digits of x read the same in both directions. Negative numbers and any positive number ending in 0 (other than 0 itself) are not palindromes.

Inputx = 1221

Outputtrue

Pop the last digit of x and push it onto a reversed half. Stop when x ≤ rev. Then rev equals x or rev/10 equals x (odd-length case).

def is_palindrome(x):
    if x < 0 or (x % 10 == 0 and x != 0):
        return False
    rev = 0
    while x > rev:
        rev = rev * 10 + x % 10
        x //= 10
    return x == rev or x == rev // 10

function isPalindrome(x) {
  if (x < 0 || (x % 10 === 0 && x !== 0)) return false;
  let rev = 0;
  while (x > rev) {
    rev = rev * 10 + (x % 10);
    x = Math.floor(x / 10);
  }
  return x === rev || x === Math.floor(rev / 10);
}

class Solution {
    public boolean isPalindrome(int x) {
        if (x < 0 || (x % 10 == 0 && x != 0)) return false;
        int rev = 0;
        while (x > rev) {
            rev = rev * 10 + x % 10;
            x /= 10;
        }
        return x == rev || x == rev / 10;
    }
}

bool isPalindrome(int x) {
    if (x < 0 || (x % 10 == 0 && x != 0)) return false;
    int rev = 0;
    while (x > rev) {
        rev = rev * 10 + x % 10;
        x /= 10;
    }
    return x == rev || x == rev / 10;
}

Time: O(log₁₀ x) Space: O(1)