设计一个简单的矩阵C++迭代器

#include <iostream>
#include <vector>

class Matrix {
public:
    using value_type = int;
    using size_type = std::size_t;
    using reference = value_type&;
    using const_reference = const value_type&;

    Matrix(size_type rows, size_type cols) : data(rows * cols), rows_(rows), cols_(cols) {}

    class Iterator {
    public:
        using iterator_category = std::random_access_iterator_tag;
        using value_type = Matrix::value_type;
        using difference_type = std::ptrdiff_t;
        using pointer = value_type*;
        using reference = value_type&;

        Iterator(pointer ptr) : ptr_(ptr) {}

        reference operator*() const { return *ptr_; }
        pointer operator->() { return ptr_; }
        Iterator& operator++() { ++ptr_; return *this; }
        Iterator operator++(int) { Iterator tmp = *this; ++ptr_; return tmp; }
        friend bool operator== (const Iterator& a, const Iterator& b) { return a.ptr_ == b.ptr_; };
        friend bool operator!= (const Iterator& a, const Iterator& b) { return a.ptr_ != b.ptr_; };

    private:
        pointer ptr_;
    };

    Iterator begin() { return Iterator(&data[0]); }
    Iterator end() { return Iterator(&data[rows_ * cols_]); }

    reference operator()(size_type row, size_type col) { return data[row * cols_ + col]; }
    const_reference operator()(size_type row, size_type col) const { return data[row * cols_ + col]; }

private:
    std::vector<value_type> data;
    size_type rows_;
    size_type cols_;
};

int main() {
    Matrix mat(3, 3);
    int count = 0;
    for (auto& elem : mat) {
        elem = count++;
    }

    for (size_t i = 0; i < 3; ++i) {
        for (size_t j = 0; j < 3; ++j) {
            std::cout << mat(i, j) << " ";
        }
        std::cout << std::endl;
    }

    return 0;
}