识别2D向量C ++中的位置

Question

I'm really struggling with vectors. Although I could do this in an array, I need to be able to pass my grid into a function without constant rows and columns.

    for (row = matrix.begin(); row != matrix.end(); ++row)
{
    for (col = row->begin(); col != row->end(); ++col)
    {
        //I need to do stuff like if (matrix[row-1][col+1] == blah)
    }
}

Thank you!

Answer 1

You can use the functions out of <iterator> to find adjacent items

#include <iterator>

auto prev_row = std::prev(row);
auto next_row = std::next(row);

Similarly

auto prev_cell = std::prev(col);
auto next_cell = std::next(col);

Just be careful with your loop start and end values so that you do not go out of bounds, ie make sure std::prev does not go before begin() and make sure std::next doesn't advance you to end() .

Answer 2

std::vector supports indexing so you don't have to use iterators. You can do something like this:

std::vector<std::vector<int>> matrix; 
std::vector<int> row;
row.push_back(1);
row.push_back(2);
matrix.push_back(row);
for (int row = 0; row < matrix.size(); ++row) {
    for (int col = 0; col < matrix[row].size(); ++col) {
        std::cout << matrix[row][col] << std::endl;
    }
}