Question

How to change all elements of row i and column j in a binary matrix to 0 if cell[i, j] is 0 with C++

Answer 1

#include <iostream>
#include <vector>

void printMatrix(std::vector<std::vector<int>> const &matrix) {
    for (auto &row: matrix) {
        for (auto &val: row) {
            std::cout << val << " ";
        }
        std::cout << "\n";
    }
    std::cout << "\n";
}
 
void changeRowColumn(std::vector<std::vector<int>> &matrix, int row, int col) {
    int rows = matrix.size();
    int cols = matrix[0].size();
    
    // -1 = different from the existing zeros
    for (int j = 0; j < cols; j++) {
        if (matrix[row][j] != 0) {
            matrix[row][j] = -1;
        }
    }
    
    for (int i = 0; i < rows; i++) {
        if (matrix[i][col] != 0) {
            matrix[i][col] = -1;
        }
    }
}
 
void changeBinaryMatrix(std::vector<std::vector<int>> &matrix) {
    if (matrix.size() == 0) {
        return;
    }
 
    int rows = matrix.size();
    int cols = matrix[0].size();
 
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            if (matrix[i][j] == 0) {
                changeRowColumn(matrix, i, j);
             }
        }
    }
    
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            if (matrix[i][j] == -1) {
                matrix[i][j] = 0;
            }
        }
    }
}
 
int main()
{
    std::vector<std::vector<int>> matrix =
    {
        { 1, 1, 0, 1, 1, 1 },
        { 1, 1, 1, 1, 1, 1 },
        { 1, 1, 0, 1, 1, 1 },
        { 1, 1, 1, 1, 1, 1 },
        { 1, 0, 1, 1, 1, 1 }
    };
 
    changeBinaryMatrix(matrix);
 
    printMatrix(matrix);
}



/*
run:

0 0 0 0 0 0 
1 0 0 1 1 1 
0 0 0 0 0 0 
1 0 0 1 1 1 
0 0 0 0 0 0 

*/

 

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Answer 2

#include <iostream>

#define COLS 6

void changeRowColumn(int matrix[][COLS], int rows, int cols, int row, int col) {
    // -1 = different from the existing zeros
    
    for (int j = 0; j < cols; j++) {
        if (matrix[row][j] != 0) {
            matrix[row][j] = -1;
        }
    }
    
    for (int i = 0; i < rows; i++) {
        if (matrix[i][col] != 0) {
            matrix[i][col] = -1;
        }
    }
}

void changeBinaryMatrix(int matrix[][COLS], int rows, int cols) {
    if (rows == 0 || cols == 0) {
        return;
    }
    
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            if (matrix[i][j] == 0) {
                changeRowColumn(matrix, rows, cols, i, j);
            }
        }
    }
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            if (matrix[i][j] == -1) {
                matrix[i][j] = 0;
            }
        }
    }
}

void printMatrix(int matrix[][COLS], int rows, int cols) {
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            std::cout << matrix[i][j] << " ";
        }
        std::cout << "\n";
    }
}

int main() {
    int matrix[][COLS] = {
            { 1, 1, 0, 1, 1, 1 },
            { 1, 1, 1, 1, 1, 1 },
            { 1, 1, 0, 1, 1, 1 },
            { 1, 1, 1, 1, 1, 1 },
            { 1, 0, 1, 1, 1, 1 }
    };
 
    int rows = (sizeof(matrix) / sizeof(matrix[0]));
    int cols = (sizeof(matrix) / sizeof(matrix[0][0])) / rows;
    
    changeBinaryMatrix(matrix, rows, cols);

    printMatrix(matrix, rows, cols);
}




/*
run:

0 0 0 0 0 0 
1 0 0 1 1 1 
0 0 0 0 0 0 
1 0 0 1 1 1 
0 0 0 0 0 0 

*/

 

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