Question

我正在对数组进行排序，需要将这些值的指针存储到原始索引位置。建议的方法是什么？

简化示例：

float myArray[4] = {0.1, 0.4, 0.3, 0.2}
std::sort(myArray, myArray + 4, std::greater<float>());

结果：

{0.4, 0.3, 0.2, 0.1}

现在读0.4时，我需要知道这是第一个数组中的第二个元素。我该怎么做呢？

Answer 1

也许如果效率不是真正的问题，你可以只执行手动排序并使用另一个“指针”数组（这不是真正的指针）像这样的东西：

int i, j;
float myArray[4] = {0.1, 0.4, 0.3, 0.2};
int index[4] = {0, 1, 2, 3};

for (i=0; i<4; i++)
    for (j=i+1; j<4; j++)
        if (myArray[i] < myArray[j])
        {
            fswap(&myArray[i], &myArray[j]);
            swap(&index[i], &index[j]);
        }

Answer 2

我想可能会创建一个指针数组并对指针数组（lambda）进行排序。不确定这对你是否有用。

#include <iostream>
#include <algorithm>

using namespace std;

int main(void) {

    float myArray[4] = {0.1, 0.4, 0.3, 0.2};
    float *myPointers[4];

    for (int i = 0; i < 4; i++)
        myPointers[i] = &myArray[i];

    sort(myPointers, myPointers + 4, [&] (float *a, float *b) {
        return *a > *b;
    });

    // myArray
    for (auto f : myArray)
        cout << f << endl;

    cout << endl;

    // myPointers
    for (auto f : myPointers)
        cout << *f << endl;

    cout << endl;

    // Check the address of elements
    cout << (myArray == myPointers[3]) << endl;
    cout << (myArray + 1 == myPointers[0]) << endl;
    cout << (myArray + 2 == myPointers[1]) << endl;
    cout << (myArray + 3 == myPointers[2]) << endl;

    cout << endl;

    // Indices of elements
    cout << myPointers[0] - myArray << endl;
    cout << myPointers[1] - myArray << endl;
    cout << myPointers[2] - myArray << endl;
    cout << myPointers[3] - myArray << endl;

    return 0;
}

Answer 3

只是想在这里添加更像C ++的东西

#include <iostream>
#include <utility>
#include <vector>
#include <algorithm>

using namespace std;

template<typename T, typename Cmp>
vector<pair<T,size_t>> sorted_with_indices(const vector<T> &vec, const Cmp &comparator) {
    vector<pair<T,size_t>> sorted;
    sorted.reserve(vec.size());
    for (size_t i = 0; i < vec.size(); ++i) {
        sorted.push_back(make_pair(vec[i], i));
    }

    auto cmp = [&](pair<T,size_t> a, pair<T,size_t> b) {
        return comparator(a.first, b.first);
    };

    sort(begin(sorted), end(sorted), cmp);

    return sorted;
}

int main() {

    vector<float> numbers = {0.4, 0.1, 0.3, 0.2};

    auto sorted = sorted_with_indices(numbers, greater<float>());    

    for (const auto& el : sorted) {
        cout << el.first << ' ' << el.second << endl;
    }

    return 0;
}

将指针从数组值存储到原始数组索引位置

3 个答案: