2

我正在学习 C++，我的任务是创建数组 [n] [m]，用整数填充它，然后
"Characteristic of matrix rows is called the sum of its positive even elements. You need to sort the rows of the matrix in accordance with the growth of characteristics."

这是我的代码

#include "stdafx.h"
using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
srand((unsigned)time(NULL));

int n, m;
cout << "n = ";
cin >> n;
cout << "m = ";
cin >> m;

int ** mas = new int * [n];
for (int i = 0; i < n; ++i)
{
    mas[i] = new int[m];
}

cout << "Array:\n";
for (int i = 0; i < n; ++i)
{
    for (int j = 0; j < m; ++j)
    {
        mas[i][j] = rand()%41-20;
        cout << mas[i][j] << "\t";
    }
    cout << "\n";
}

double * characteristic = new double[n];
for (int i = 0; i < n; ++i)
{
    characteristic[i] = 0;
}

for (int i = 0; i < n; ++i)
{
    for (int j = 0; j < m; ++j)
    {
        if((j%2 == 0) && (mas[i][j] >= 0)) 
        {
                characteristic[i] += mas[i][j];
        }
    }
}

cout << "Characteristics:\n";
for (int i = 0; i < n; ++i)
{
    cout << characteristic[i] << " ";
}
cout << "\n";

for (int i = 0; i < n - 1; ++i)
{
    int min = i;
    for (int j = i + 1; j < n; ++j)
    {
        if (characteristic[min] <= characteristic[j]) continue;
        min = j;
    }
    if (min != i)
    {
        double temp = characteristic[i];
        characteristic[i] = characteristic[min];
        characteristic[min] = temp;

        for (int k = 0; k < m; ++k)
        {
            int temp1 = mas[i][k];
            mas[i][k] = mas[min][k];
            mas[min][k] = temp1;
        }

    }
}

cout << "\nSorted characteristics:\n";
for (int i = 0; i < n; ++i)
{
    cout << characteristic[i] << " ";
}
cout << "\n";

cout << "Sorted array:\n";
for (int i = 0; i < n; ++i)
{
    for (int j = 0; j < m; ++j)
    {
        cout << mas[i][j] << "\t";
    }
    cout << "\n";
}

for (int i = 0; i < n; ++i)
{
    delete [] mas[i];
}
delete [] mas;

delete [] characteristic;

system("PAUSE");
return 0;
}

我为特征创建了另一个数组，并同时对它和第一个数组进行了排序，但似乎我使用了太难的方法来完成给定的任务。也许还有其他方法？

4

3 回答 3

3

您是否也想使用与“特征”相同的顺序对矩阵进行排序？

假设您有 C++ 风格的代码来计算特征：

std::vector<double> characteristic(n, 0.0);
std::transform(begin(mas), end(mas), begin(characteristic), sum_);

然后你可以对它们进行排序：

std::sort(begin(characteristic), end(characteristic));

或者你可以，确实立即对矩阵进行排序：

std::sort(begin(mas), end(mas), [&sum_](int_vec const& a, int_vec const& b) 
         { return sum_(a)<sum_(b); });

编辑修复了所有版本以使用正确的“特征总和”（尽管保留名称），谢谢@Adam

这是一个完整的程序来演示这一点：在 Coliru 上实时观看

#include <random>
#include <iostream>
#include <string>
#include <vector>

#include <cstdlib>
#include <algorithm>
#include <iterator>

using namespace std;

int main()
{
    typedef std::vector<int> int_vec;

    srand((unsigned)time(NULL));
    int n, m;
    cout << "n = ";
    cin  >> n;
    cout << "m = ";
    cin  >> m;

    std::vector<int_vec> mas(n, int_vec(m));

    for (auto& v : mas)
        std::for_each(begin(v), end(v), [](int& i) { i = rand()%41-20; });

    cout << "Array:\n";
    for (auto const& v : mas)
    {
        std::copy(begin(v), end(v), ostream_iterator<int>(cout, "\t"));
        cout << "\n";
    }

    auto sum_ = [m](int_vec const& v) { 
        double vchar = 0;
        for (auto j = 0; j < m; j+=2)
            if(v[j] >= 0) vchar += v[j];
        return vchar;
    };

    std::vector<double> characteristic(n, 0.0);
    std::transform(begin(mas), end(mas), begin(characteristic), sum_);

    cout << "Characteristics:\n";
    std::copy(begin(characteristic), end(characteristic), ostream_iterator<double>(cout, " "));
    cout << "\n";

    std::sort(begin(characteristic), end(characteristic));

    cout << "\nSorted characteristics:\n";
    std::copy(begin(characteristic), end(characteristic), ostream_iterator<double>(cout, " "));
    cout << "\n";

    std::sort(begin(mas), end(mas), [&sum_](int_vec const& a, int_vec const& b) { return sum_(a)<sum_(b); });

    cout << "Sorted Array:\n";
    for (auto const& v : mas)
    {
        std::copy(begin(v), end(v), ostream_iterator<int>(cout, "\t"));
        cout << "\n";
    }

}

样本输出：

n = m = Array:
11  15  19  18  
-20 -16 2   -11 
8   2   19  8   
Characteristics:
30 2 27 

Sorted characteristics:
2 27 30 
Sorted Array:
-20 -16 2   -11 
8   2   19  8   
11  15  19  18
于 2013-10-11T07:07:31.453 回答
1

@sehe 为您提供了很好的建议，但我怀疑在您了解更多 C++ 之前，很多这些东西都没有意义。

这是消除慢循环的简单改进：

在进行行交换时，交换行指针，而不是复制它们指向的每个值。替换这个：

    for (int k = 0; k < m; ++k)
    {
        int temp1 = mas[i][k];
        mas[i][k] = mas[min][k];
        mas[min][k] = temp1;
    }

和：

    int* temp1 = mas[i];
    mas[i] = mas[min];
    mas[min] = temp1;

如果您能弄清楚如何使用内置排序算法，那将是在此基础上的另一项改进，但即使是这个小小的改变也会让您受益匪浅。

于 2013-10-11T09:12:45.623 回答
0

由于大小 n,m 在编译时是已知的，因此您可以使用qsortC 库中的函数。

#include <stdlib.h>

void qsort(void *base, size_t nmemb, size_t size,
           int (*compar)(const void *, const void *));

where iscompar是您编写的函数，它应该将其两个参数都视为指向矩阵行的指针。然后它可以计算两行的特征，并根据哪一行的特征更大返回-1、0或1。

于 2013-10-11T06:54:26.463 回答