Removing a Vector Element: Stable vs Swap Removal

Question 48 / 51 • Correct so far: 0 (0 answered)

Snippet A

Erase Middle

void removeMany(std::vector<int>& v, std::size_t count) {
    for (std::size_t i = 0; i < count; ++i) {
        std::size_t pos = v.size() / 2;
        v.erase(v.begin() + static_cast<std::ptrdiff_t>(pos));
    }
}

removeMany(v, kRemovalsPerRun);
Snippet B

Swap Pop

void removeMany(std::vector<int>& v, std::size_t count) {
    for (std::size_t i = 0; i < count; ++i) {
        std::size_t pos = v.size() / 2;
        std::swap(v[pos], v.back());
        v.pop_back();
    }
}

removeMany(v, kRemovalsPerRun);
Shared test data (shared-setup) 
constexpr std::size_t kVecSize = 8192;
constexpr std::size_t kRemovalsPerRun = 1024;

static std::vector<int> makeData() {
    std::vector<int> v(kVecSize);
    std::iota(v.begin(), v.end(), 0);
    return v;
}

static const std::vector<int> ORIGINAL = makeData();

Which snippet is faster?

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