c++ - 使用 std::sort 对二维数组进行排序(基于列)

Question

我正在运行一个测试，显示按列对二维数组进行排序的好处，方法是将数据提取到一个单独的数组中并对该数组进行排序，然后将其复制回该列。我想运行 std::sort 作为每次运行的排序算法。我试图弄清楚如何先在适当的位置运行循环，然后再进入二维阵列的复制和复制。输入/输出的一个例子是这样的。

#include <iostream>
#include <algorithm>

int main() {
    int input[][5] =  { { 13, 27, 4 , 1 , 11 },
                        { 11, 19, 2 , 37, 1  },
                        { 32, 64, 11, 22, 41 },
                        { 71, 13, 27, -8, -2 },
                        { 0 , -9, 11, 99, 13 } };

    // std::sort something here.

    int output[][5] = { { 0 , -9, 2 , -8, -2 },
                        { 11, 13, 4 , 1 , 1  },
                        { 13, 19, 11, 22, 11 },
                        { 32, 27, 11, 37, 13 },
                        { 71, 64, 27, 99, 41 } };                      
    return 0;
}

感谢您的帮助。

Answer 1

您可以编写自己的迭代器，例如:

#include <iterator>

template<typename Container>
class column_iterator : public std::iterator<std::random_access_iterator_tag,
                                            typename std::decay<decltype(std::declval<Container>()[0][0])>::type>
{
    typedef typename Container::iterator iterator;
    typedef typename std::decay<decltype(std::declval<Container>()[0][0])>::type type;
public:

    column_iterator(iterator it, int n) : it(it), n(n) {}

    column_iterator& operator++() {++it; return *this;}
    column_iterator& operator++(int) { auto res(*this); ++*this; return res;}
    column_iterator& operator +=(std::ptrdiff_t offset) { it += offset; return *this;}
    column_iterator operator +(std::ptrdiff_t offset) const { auto res(*this); res += offset; return res;}

    column_iterator& operator--() {--it; return *this;}
    column_iterator& operator--(int) { auto res(*this); --*this; return res;}
    column_iterator& operator -=(std::ptrdiff_t offset) { it -= offset; return *this;}
    column_iterator operator -(std::ptrdiff_t offset) const { auto res(*this); res -= offset; return res;}

    type& operator*() { return (*it)[n];}
    type* operator->() { return &(it)[n];}

    bool operator == (const column_iterator& rhs) const { return it == rhs.it && n == rhs.n; }
    bool operator != (const column_iterator& rhs) const { return !(*this == rhs); }
    bool operator < (const column_iterator& rhs) const { return it < rhs.it; }

    std::ptrdiff_t operator -(const column_iterator& rhs) const { return it - rhs.it; }

private:
    iterator it;
    int n;
};

template<typename Container>
column_iterator<Container> begin(Container& cont, int n)
{
    return column_iterator<Container>(cont.begin(), n);
}

template<typename Container>
column_iterator<Container> end(Container& cont, int n)
{
    return column_iterator<Container>(cont.end(), n);
}

现在，让我们测试一下:

#include <algorithm>
#include <array>
#include <iostream>
#include <vector>
#include <cassert>

void display(const std::vector<std::array<int, 5>>& v)
{
    for (auto rows : v) {
        for (auto elem : rows) {
            std::cout << elem << " ";
        }
        std::cout << std::endl;
    }
}

int main() {
    std::vector<std::array<int, 5>> input {
                        {{ 13, 27, 4 , 1 , 11 }},
                        {{ 11, 19, 2 , 37, 1  }},
                        {{ 32, 64, 11, 22, 41 }},
                        {{ 71, 13, 27, -8, -2 }},
                        {{ 0 , -9, 11, 99, 13 }} };

    for (int i = 0; i != 5; ++i) {
        std::sort(begin(input, i), end(input, i));
    }

    display(input);

    const std::vector<std::array<int, 5>> output {
                        {{ 0 , -9, 2 , -8, -2 }},
                        {{ 11, 13, 4 , 1 , 1  }},
                        {{ 13, 19, 11, 22, 11 }},
                        {{ 32, 27, 11, 37, 13 }},
                        {{ 71, 64, 27, 99, 41 }} };

    assert(input == output);
    return 0;
}