cppLogic errorMedium

Reverse vector with signed/unsigned comparison issue

Time: 0:00

BugFind the bug and fix the code

What it should do

Reverse elements of vector in place. Example: reverseSliceVector([1, 2, 3]) -> [3, 2, 1]

What happens instead

Infinite loop or out-of-bounds access with unsigned index underflow

#include <iostream>
#include <vector>

std::vector<int> reverseSliceVector(std::vector<int> nums) {
    if (nums.empty()) return nums;
    // size_t is unsigned; when right passes 0, it wraps to 18446744073709551615
    for (size_t left = 0, right = nums.size() - 1; left < right; ++left, --right) {
        std::swap(nums[left], nums[right]);
    }
    return nums;
}

int main() {
    std::vector<int> res = reverseSliceVector({1, 2, 3});
    return 0;
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

<iframe src="https://trybughunt.com/embed/198a3de9-3e16-449e-afed-4cdca4234278" title="Debugging challenge: Reverse vector with signed/unsigned comparison issue" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe> <p style="font-size:14px">Debugging challenge from <a href="https://trybughunt.com/challenges/198a3de9-3e16-449e-afed-4cdca4234278">TryBugHunt</a></p>

#include <iostream> #include <vector> std::vector<int> reverseSliceVector(std::vector<int> nums) { if (nums.empty()) return nums; // size_t is unsigned; when right passes 0, it wraps to 18446744073709551615 for (size_t left = 0, right = nums.size() - 1; left < right; ++left, --right) { std::swap(nums[left], nums[right]); } return nums; } int main() { std::vector<int> res = reverseSliceVector({1, 2, 3}); return 0; }

Reverse vector with signed/unsigned comparison issue

What it should do

What happens instead

More logic errors to practise

Reverse vector with signed/unsigned comparison issue

What it should do

What happens instead

More logic errors to practise