…
if (matrix.empty()) return;
int n = matrix.size(), m = matrix[0].size();
int col0 = 1, row0 = 1;
for (int i = 0; i < n; i )
if (!matrix[i][0]) col0 = 0;
for (int i = 0; i < m; i )
if (!matrix[0][i]) row0 = 0;
for (int i = 1; i < n; i )
for (int j = 1; j < m; j )
if (!matrix[i][j])
{
matrix[i][0] = 0;
matrix[0][j] = 0;
}
for (int i = 1; i < n; i )
if (!matrix[i][0])
for (int j = 1; j < m; j )
matrix[i][j] = 0;

    for (int i = 1; i < m; i ++ )
        if (!matrix[0][i])
            for (int j = 1; j < n; j ++ )
                matrix[j][i] = 0;

    if (!col0)
        for (int i = 0; i < n; i ++ )
            matrix[i][0] = 0;

    if (!row0)
        for (int i = 0; i < m; i ++ )
            matrix[0][i] = 0;
}
...