Is Reverse Integer easy or hard?

Reverse Integer is generally classified as a medium problem because of the overflow constraint. Reversing digits itself is simple, but correctly detecting overflow without using larger numeric types requires careful boundary checks.

Reverse Integer Python/Java solution

In Python or Java, the arithmetic solution repeatedly extracts digits using modulus and builds the reversed number with multiplication by 10. Java implementations must explicitly check 32-bit overflow using Integer.MAX_VALUE and Integer.MIN_VALUE. Python still needs manual boundary checks to match the problem constraints.

How to solve Reverse Integer in O(n)?

Treat n as the number of digits in the integer. Repeatedly extract digits using modulus, build the reversed number using multiplication by 10, and check for overflow before each update. The loop runs once per digit, giving O(n) time and O(1) extra space.

What is the best approach for Reverse Integer?

The best approach uses iterative division and modulus. Extract the last digit with x % 10, append it to the reversed number using rev = rev * 10 + digit, and shrink the original number with integer division. Add overflow checks before multiplying by 10. This runs in O(d) time and O(1) space where d is the number of digits.

Is Reverse Integer asked at Google/Amazon/Meta?

Reverse Integer is a common screening-level problem used by companies like Amazon, Google, and Meta to test understanding of integer manipulation, overflow handling, and basic algorithmic reasoning. Variants appear in phone screens and coding assessments.

What data structure is used in Reverse Integer?

The optimal solution does not require any data structure. It relies purely on arithmetic operations such as modulus and integer division. The alternative implementation uses strings for digit reversal, which introduces extra memory usage.

What is the time complexity of Reverse Integer?

The time complexity is O(d), where d is the number of digits in the integer. Each iteration processes one digit using modulus and division. Since a 32-bit integer has at most 10 digits, the operation effectively runs in constant time.

Description Solution Video 13:12

7. Reverse Integer

Medium32.2% acceptance22 companies

Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-2³¹, 2³¹ - 1], then return 0.

Assume the environment does not allow you to store 64-bit integers (signed or unsigned).

Example 1: