C++ 矩阵 - 最小/最大元素

Question

我实现了可以找到矩阵元素的 c++ 程序： 哪个是行的最大元素，同时是其列的最小元素，或者 - 行的最小元素，同时是其列的最大元素。 例如，我们有 data.txt 文件：

• 4
• 7 8 9 10
• 6 5 4 11
• 5 0 1 12
• 4 2 7 13
-

其中 4 是 n - 矩阵大小 (4x4)，7 和 10 是这些数字。

代码如下：

#include <iostream>
#include <fstream>

using namespace std;
int main(){

    ifstream is;
    ofstream os;
    int n;

    is.open("data.txt");
    if (is.fail()){
        cout << "Failed to open data file" << endl;
        exit(-1);
    }
    is >> n;

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

    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            is >> matrix[i][j];
        }
    }

    double* maxROW = new double[n];
    double* minROW = new double[n];
    for (int i = 0; i < n; i++){
        maxROW[i] = matrix[i][0];
        minROW[i] = matrix[i][0];
        for (int j = 0; j < n; j++){
            if (matrix[i][j] > maxROW[i]){
                maxROW[i] = matrix[i][j];
            }
            if (matrix[i][j] < minROW[i]){
                minROW[i] = matrix[i][j];
            }
        }
    }

    double* maxCOLUMN = new double[n];
    double* minCOLUMN = new double[n];
    int x = 0;
    for (int i = 0; i < n; i++){
        maxCOLUMN[i] = matrix[0][x];
        minCOLUMN[i] = matrix[0][x];
        for (int j = 0; j < n; j++){
            if (matrix[j][i] > maxCOLUMN[i]){
                maxCOLUMN[i] = matrix[j][i];
            }
            if (matrix[j][i] < minCOLUMN[i]){
                minCOLUMN[i] = matrix[j][i];
            }

            if (j == n - 1) x++;
        }
    }

    int k = 0;
    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            if (maxROW[i] == minCOLUMN[j]){
                k++;
            }
            if (minROW[i] == maxCOLUMN[j]){
                k++;
            }
        }
    }

    double* matrixNUM = new double[k];
    int l = 0;
    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            if (maxROW[i] == minCOLUMN[j]){
                matrixNUM[l] = matrix[i][j];
                l++;
            }
            if (minROW[i] == maxCOLUMN[j]){
                matrixNUM[l] = matrix[i][j];
                l++;
            }
        }
    }

    cout << "Matrix numbers: " << endl;
    for (int i = 0; i < k; i++){
        cout << matrixNUM[i] << ", ";
    }
    cout << endl;

    for (int i = 0; i < n; i++){
        delete[] matrix[i];
    }
    delete[] matrix;
    delete[] maxCOLUMN;
    delete[] minCOLUMN;
    delete[] maxROW;
    delete[] minROW;
    delete[] matrixNUM;
    return 0;
}

问题：我想知道我的代码是否是“脏”代码？因为我总是热衷于让一切变得如此困难，只要有可能让它变得容易。是否有不同的方式，也许更容易，也许更容易理解的方式来实现这样的任务？提前感谢谁会发现此代码中的错误。

Answer 1

int main(){

  std::ifstream is;
  std::ofstream os;

  is.open("data.txt");
  if (is.fail()){
    std::cerr << "Failed to open data file\n";
    exit(-1);
  }
  int n;
  is >> n;

  if (n <= 0)
  {
    std::cerr << "Negative matrix size, aborting\n";
    exit(-1);
  }
  std::vector< std::vector<double> > matrix( n, std::vector<double>(n) );

  for (int i = 0; i < n; i++){
    for (int j = 0; j < n; j++){
      is >> matrix[i][j];
    }
  }

  std::vector<double> maxROW(n);
  std::vector<double> minROW(n);
  for (int i = 0; i < n; i++){
    auto minmax = std::minmax_element( matrix[i].begin(), matrix[i].end() );
    maxROW[i] = *minmax.second;
    minROW[i] = *minmax.first;
  }

  std::vector<double> maxCOLUMN(n);
  std::vector<double> minCOLUMN(n);
  for (int i = 0; i < n; i++){
    maxCOLUMN[i] = matrix[0][i];
    minCOLUMN[i] = matrix[0][i];
    for (int j = 1; j < n; j++){
      maxCOLUMN[i] = std::max( maxCOLUMN[i], matrix[j][i] );
      minCOLUMN[i] = std::min( minCOLUMN[i], matrix[j][i] );
    }
  }

  std::vector<double> matrixNUM;
  for (int i = 0; i < n; i++){
    for (int j = 0; j < n; j++){
      if (maxROW[i] == minCOLUMN[j]){
        matrixNUM[l].push_back(matrix[i][j]);
      }
      if (minROW[i] == maxCOLUMN[j]){
        matrixNUM[l].push_back(matrix[i][j]);
      }
    }
  }

  std::cout << "Matrix numbers: " << endl;
  for (double num:matrixNUM)
    std::cout << num << ", ";
  }
  std::cout << "\n";
}

可能有错别字，但上面应该一样快，而且代码更少。

它确实使用了一些 C++11 特性。

Answer 2

随机说明，C++11 的变长数组处理仍然有繁琐的方面，但是：

int n;          is >> n;

double (&matrix)[n][n] = *(double(*)[n][n])(new double[n*n]);

for (auto &r:matrix)
        for (auto &c:r)
                is >> c;

// ...

delete[] &matrix

堆得很好。