std::list Traversal: Forward vs Two-Ended

Question 3 / 12 • Correct so far: 0 (0 answered)

Snippet A

List Forward

std::uint64_t sumList(const std::list<std::uint64_t>& items) {
    std::uint64_t sum = 0;
    for (std::uint64_t value : items)
        sum += value;
    return sum;
}

std::uint64_t result = sumList(values);
Snippet B

List Two Ended

std::uint64_t sumList(const std::list<std::uint64_t>& items) {
    if (items.empty())
        return 0;

    std::uint64_t sum = 0;
    auto left = items.begin();
    auto right = std::prev(items.end());

    while (left != right && std::next(left) != right) {
        sum += *left;
        sum += *right;
        ++left;
        --right;
    }

    sum += *left;
    if (left != right)
        sum += *right;

    return sum;
}

std::uint64_t result = sumList(values);
Shared test data (shared-setup) 
constexpr std::size_t LIST_SIZE = 1 << 15;
static std::list<std::uint64_t> values;

struct ListInit {
    ListInit() {
        for (std::size_t index = 0; index < LIST_SIZE; ++index)
            values.push_back((index * 1315423911u) ^ (index << 7));
    }
} _list_init;

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