# Question

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

Example 1:

Input: 121
Output: true


Example 2:

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


# Solution

Use String:

class Solution:
def isPalindrome(self, x):
"""
:type x: int
:rtype: bool
"""
s = str(x)
if len(s) % 2 != 0:
left, right = len(s) // 2, len(s) // 2
else:
left, right = len(s) // 2 - 1, len(s) // 2

while left >= 0:
if s[left] != s[right]:
return False
else:
left -= 1
right += 1

return True


Without string conversion:

import math

class Solution:
def isPalindrome(self, x):
"""
:type x: int
:rtype: bool
"""
if 0 <= x <= 9:
return True
elif x < 0:
return False

digits = math.floor(math.log(x, 10)) + 1
stack = list()

for count in range(0, digits):
digit = x % 10
x //= 10
if count < digits // 2:
stack.append(digit)
elif count == digits // 2:
if digits % 2 == 0:
matching_digit = stack.pop()
if digit != matching_digit:
return False
else:
matching_digit = stack.pop()
if digit != matching_digit:
return False

return True