Palindrome Number🎙

Question

Given an integer x, return true if x is palindrome integer.

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

• For example, 121 is a palindrome while 123 is not.

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?

Java Solution

Three different solutions with three different time complexities

O(n)
Where n is the number of digits. The reversing of a string will take n steps.

Code

O(n/2)
Where n is the number of digits.

Code

O(Log base 10 (n))
Where n is the number itself, in the below program we are trying to get the half number of the actual number, and on each loop, we are dividing out input by 10. In other words how many times do we have to divide n by 10 in order to get its half number

Code