如何获得2d std :: vector（`std :: vector< std :: vector< T>>`）的第N个元素？
问题描述：
我们给出了一些 int el_position 数字，这是我们的第二个向量（ std :: vector< ; std :: vector< int> matrix（5，std :: vector< int>（4）））。
We are given some int el_position number which is a position of wanted by us element in flatened representation of our 2d vector (std::vector< std::vector<int> > matrix(5, std::vector<int>(4))).
如果我们有这样的矩阵
11 21 31 41 51
61 71 81 91 101
我们得到 el_position code> 7 我们需要得到第二行的第二个元素。是可能做这样的事与stl 2d矢量？
and we were given el_position == 7 we would need to get second element of second row. Is it possible to do such thing withstd stl 2d vector? How to get value of element by given its position in flattened array?
答
当然，这是可能的：
row = el_position % row_length;
col = el_position / row_length;