Reverse Integer - Video Solutions

Problem Overview: Reverse the digits of a signed 32-bit integer x. If reversing the digits causes the value to go outside the 32-bit signed integer range [-2^31, 2^31 - 1], return 0. Negative numbers must preserve their sign after reversal.

Approach 1: Iterative Division and Modulus (Time: O(d), Space: O(1))

This approach processes the integer digit by digit using arithmetic operations. Repeatedly extract the last digit using x % 10, append it to a new number using rev = rev * 10 + digit, and remove the last digit from the original number with integer division x //= 10. The key challenge is detecting overflow before it happens. You check whether rev will exceed the 32-bit boundary before multiplying by 10. This solution uses constant space and avoids converting the number to a string, making it the standard arithmetic solution expected in interviews involving math and integer manipulation.

Approach 2: String Conversion and Manipulation (Time: O(d), Space: O(d))

This approach converts the integer to a string, reverses the characters, and converts the result back to an integer. Handle the negative sign separately: store it, reverse the remaining digits, then reapply the sign. After conversion, verify the result still falls within the 32-bit signed integer range. This method is simpler to implement and easier to reason about, but it uses extra memory for the string and relies on built-in string operations from languages such as Python or JavaScript. It demonstrates basic manipulation of strings rather than pure math operations.

Recommended for interviews: The iterative division and modulus approach is the one interviewers expect. It shows you understand integer digit extraction, overflow detection, and constant-space arithmetic. The string method is acceptable for quick implementations, but the arithmetic solution demonstrates stronger algorithmic control over numeric operations.