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The problem

A legacy payments system stores reference codes as signed 32-bit integers, and a new report needs each code with its digits reversed, keeping the sign. The catch: some codes reverse into numbers that no longer fit in 32 bits (reversing 1534236469 gives 9646324351), and the system has no 64-bit type available. For those, the function must return 0 instead of silently wrapping around. So the real problem is detecting overflow before it happens, using only 32-bit arithmetic.

Example: 123 → 321, -123 → -321, 120 → 21, 1534236469 → 0.

Function signature

int reverse(int x);  // reversed digits with the same sign, or 0 if the result overflows int

Test cases

Input x	Output	Explanation
123	321
-123	-321	The sign is kept
120	21	Trailing zeros become leading zeros and vanish
0	0
1534236469	0	Reversed value 9646324351 exceeds INT_MAX
-2147483648	0	Reversed value −8463847412 is below INT_MIN
1463847412	2147483641	Fits just under INT_MAX (2147483647)

(Confirm: the environment can't store 64-bit integers, so overflow must be detected with 32-bit checks; return 0 on overflow.)

How interviewers phrase it

• "Reverse the digits of a 32-bit signed integer. Return 0 if it overflows" (LeetCode 7).
• A simpler version without the overflow rule: "Reverse a number," often a first-round warm-up.
• The follow-up that matters: "Assume you can't use long long. How do you detect overflow?"

Clarifying questions to ask

1. What should happen on overflow: return 0, throw, or saturate?
2. Am I allowed to use a 64-bit type?
3. How are negative numbers handled: keep the sign?
4. Should trailing zeros disappear (120 → 21)?

Follow-ups to expect

1. "How do you detect overflow without 64-bit arithmetic?"
2. "Why 7 and −8?"
3. "Why doesn't this code need special handling for negative numbers?"
4. "What if 64-bit is allowed?"
5. "Complexity?"

Related questions

• Count all Digits of a Number Easy
• Palindrome Number Easy
• GCD of Two Numbers Easy
• Check if the Number is Armstrong Easy
• Print all Divisors Easy
• Check for Prime Number Easy

All 474 dsa interview questions

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