7. Reverse Integer

https://leetcode.com/problems/reverse-integer/

Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: 123
Output: 321

Example 2:

Input: -123
Output: -321

Example 3:

Input: 120
Output: 21

Note:
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231,  231 − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

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Intuition

Catch last digit

Check overflow and underflow boundary condition

update ans

Time Complexity: O(log n) - number of digits

Space Complexity: O(1) - Constant 

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