置换2D数组中的元素

Question

I'm attempting to shift zeros of a matrix to get minors of it by using in my program 2d-array. How correctly delete (shift) elements of 2d-array?

I know how to handle this problem with 1d-array by permuting its element

for (int i = DEL; i < (SIZE - 1); i++)
    array[i] = array[i + 1];

Where DEL - index of element, which we want delete, SIZE - size of array. But I've got not the same result with multidimensional-array:

for (int i = DEL; i < (SIZE - 1); i++)
    for (int j = DEL; j < (SIZE - 1); j++)
        array[i][j] = array[i+1][j+1];

Where is a mistake?

#include <iostream>

using namespace std;

int main()
{
    int array[3][3] = {
        1, 2, 3,
        4, 5, 6, 
        7, 8, 9};

    // Setting to zero 2nd row and 3rd column
    int m = 1; // 2
    int n = 2; // 3


    for (int i = 0; i < 3; i++)
    {
        for (int j = 0; j < 3; j++)
        {
            array[m][j] = 0;
            array[i][n] = 0;
            cout << array[i][j];
            // Trying to shift every element, which equals zero
            if (array[i][j] == 0)
                for (int k = i; k < 2; k++)
                    for (int l = j; l < 2; l++)
                        array[k][l] = array[k+1][l+1];          

        }
        cout << endl;
    }



    cout << endl;

    for (int i = 0; i < 3; i++)
    {
        for (int j = 0; j < 3; j++)
            cout << array[i][j];
        cout << endl;
    }
}

I get:

120
000
780

120
000
780

But actually I want the last output be like that:

120
780
000

Answer 1

I think the term "permuting" does not fit here. You want to delete rows and columns from a 2 dimensional array.

However you made some semantic errors. I fixed this for you and show you the corrected code below.

One big advice. Try to shrink a big problem into several smaller problems. Your trying too much in multi-nested for loops. Do one after the other.

Please see:

#include <iostream>

constexpr size_t MaxArraySize = 3;

int main()
{
    int array[MaxArraySize][MaxArraySize] = {
        1, 2, 3,
        4, 5, 6,
        7, 8, 9 };

    // Setting to zero 2nd row and 3rd column
    int rowToDelete = 1; // 2
    int colToDelete = 2; // 3

    // Set cell to delete to 0
    for (int row = 0; row < MaxArraySize; ++row)
    {
        for (int col = 0; col < MaxArraySize; ++col)
        {
            array[rowToDelete][col] = 0;
            array[row][colToDelete] = 0;
            std::cout << array[row][col];
        }
        std::cout << '\n';
    }

    // First shift all rows
    for (int row = rowToDelete; row < MaxArraySize - 1; ++row)
        for (int col = 0; col < MaxArraySize; ++col)
            array[row][col] = array[row+1][col];

    // Then shift all cols
    for (int col = colToDelete; col < MaxArraySize-1; ++col)
        for (int row = 0; row < MaxArraySize; ++row)
            array[row][col] = array[row][col+1];

    // Set the cells that were shifted away to 0
    for (int row = 0; row < MaxArraySize; ++row)
        array[row][MaxArraySize - 1] = 0;
    for (int col = 0; col < MaxArraySize; ++col)
        array[MaxArraySize - 1][col] = 0;

    // Show result
    std::cout << "\n\nResult\n\n";
    for (int row = 0; row < MaxArraySize; ++row)
    {
        for (int col = 0; col < MaxArraySize; ++col)
            std::cout << array[row][col];
        std::cout << '\n';
    }
}

2nd and even more important. You are using plain C code with plain C-Style arrays. The only C++ in your code is using iostreams. That is not so good.

Try to use C++. Never ever use plain C-Style array. Try to use algorithms and containers from the STL. Use better names for variables.

The resulting piece of code will be ultra simple. And here we are really deleting rows and columns. Please see:

#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>

int main()
{
    // Lambda for printing the matric to std::cout
    auto print = [](std::vector<std::vector<int>> & m) {
        std::for_each(m.begin(), m.end(), [](std::vector<int> & vi) { std::copy(vi.begin(), vi.end(), std::ostream_iterator<int>(std::cout, " ")); std::cout << '\n'; });
    };
    // You can add whatever values. 
    std::vector<std::vector<int>> matrix {
        {11, 12, 13, 14},
        {15, 16, 17, 18},
        {19, 20, 21, 22},
        {23, 24, 25, 26}
    };
    // Show initial data
    std::cout << "\n\nInitial matrix:\n";
    print(matrix);

    constexpr size_t RowToDelete = 1; // Row 2
    constexpr size_t ColToDelete = 2; // Column3

    // Erase row
    matrix.erase(matrix.begin() + RowToDelete);
    // Erase column in each row
    std::for_each(matrix.begin(),matrix.end(), [ColToDelete](std::vector<int> & vi) { vi.erase(vi.begin() + ColToDelete); });

    // Show result
    std::cout << "\n\nResulting matrix with deleted row " << RowToDelete+1 << " and deleted column " << ColToDelete+1 << '\n';
    print(matrix);

    return 0;
}

Hope this helps . . .