Leetcode #7 — Reverse Integer (Python)

Hello everyone, today we’ll be looking at the Reverse Integer problem. This one is marked as “Easy” on Leetcode.

Problem Statement

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

Note: Assume we are dealing with an environment that 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.

Examples from Leetcode

Example 1:

Input: x = 123
Output: 321

Output Explained:

This one is pretty simple, we just need to reverse all of the digits of the given integer, so 123 will become 321.

Example 2:

Input: x = -123
Output: -321

Example 3:

Input: x = 120
Output: 21

Example 4:

Input: x = 0
Output: 0

Solution

Submission on Leetcode:

Explanation (with two examples):

1. Let's call: reverse(4567) 
- Since 4567 > 0, convert 4567 into a string, reverse that string using [::-1], and then convert the string back to an int. So result = 7654
- The number 7654 is returned because -2^31 <= 7654 <= 2^31 - 1
2. Let's call: reverse(-321)
- Since -321 < 0, take the absolute value of -321 using abs(-321), which is 321. Convert the int 321 into a string using str(-321), reverse it using [::-1] and add '-' in front of it as -321 < 0. So the string '-123' will get converted to an int once again using int('-123'). As a result, result = -123
- The number -123 is returned as -2^31 <= -123 <= 2^31 - 1

That’s all, folks! Happy learning!

Dhairya Dave