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  1. #include <utility>
  2. #include <vector>
  3. #include <algorithm>
  4. #include <iostream>
  5.  
  6. std::pair<int, int>
  7. rotated_local_next(int i, int j, int w, int h)
  8. {
  9.    if(j == 0) //top , special case top-right
  10.    {
  11.         return i == w-1 ? std::make_pair(i, ++j) : std::make_pair(++i, j);
  12.    }
  13.    if(i == w-1) //right, special case bottom-right
  14.    {
  15.         return j == h-1 ? std::make_pair(--i, j) : std::make_pair(i, ++j);
  16.    }
  17.    if(j == h-1) //bottom, special case bottom-left
  18.    {
  19.         return i == 0 ? std::make_pair(i, --j) : std::make_pair(--i, j);
  20.    }
  21.    if(i == 0) //left, special case top-left
  22.    {
  23.         return j == 0 ? std::make_pair(++i, j): std::make_pair(i, --j);
  24.    }
  25.  
  26.    // cannot happen
  27.    throw std::exception{};
  28. }
  29.  
  30. std::pair<int, int>
  31. rotated_matrix_next(int x, int y, int ring_i, int height, int width )
  32. {
  33.      auto local_point = rotated_local_next(x-ring_i, y-ring_i, width-2*(ring_i), height-2*(ring_i));
  34.      return std::make_pair(local_point.first + ring_i, local_point.second + ring_i);
  35. }
  36.  
  37. struct RingView
  38. {
  39.    RingView(std::vector<std::vector<int>>& mat, int ringnumber)
  40.    : matrix(mat)
  41.    , rows(mat.size())
  42.    , cols(mat[0].size())
  43.    , ring(ringnumber)
  44.    {}
  45.  
  46.    std::vector<std::vector<int>>& matrix;
  47.    int rows;
  48.    int cols;
  49.    int ring; // zero indexed
  50.  
  51.     class ring_iterator : public std::iterator<std::forward_iterator_tag, int>
  52.     {
  53.     public:
  54.  
  55.         ring_iterator(RingView* v = nullptr, int xpos = 0, int ypos = 0)
  56.         : view(v)
  57.         , x(xpos)
  58.         , y(ypos)
  59.         {}
  60.  
  61.         ring_iterator(const ring_iterator& other) = default;
  62.         ring_iterator(ring_iterator&& other) = default;
  63.         ring_iterator& operator =(ring_iterator const&) = default;
  64.         ring_iterator& operator=(ring_iterator&&) = default;
  65.         virtual ~ring_iterator() = default;
  66.  
  67.         RingView* view;
  68.         int x;
  69.         int y;
  70.         int holder;
  71.  
  72.         // Forward
  73.         ring_iterator& operator++() {
  74.             auto posnext = rotated_matrix_next(x, y, view->ring, view->cols, view->rows);
  75.  
  76.             x = posnext.first;
  77.             y = posnext.second;
  78.             return *this;
  79.         }
  80.  
  81.         ring_iterator operator++(int) {
  82.             auto posnext = rotated_matrix_next(x, y, view->ring, view->cols, view->rows);
  83.             ring_iterator next_iter = *this;
  84.             next_iter.x = posnext.first;
  85.             next_iter.y = posnext.second;
  86.             return next_iter;
  87.         }
  88.  
  89.         // equality required to test with end
  90.         bool operator==(const ring_iterator& other) const {
  91.             if(view == nullptr ){
  92.                 return other.view == nullptr;
  93.             }
  94.             return view->ring == other.view->ring && x == other.x && y == other.y;
  95.         }
  96.  
  97.         bool operator!=(const ring_iterator& other) const {
  98.             return !(*this == other);
  99.         }
  100.  
  101.         // usually required
  102.         int& operator*() {
  103.             return view->matrix[x][y];
  104.         }
  105.         int* operator->() {
  106.             return &(view->matrix[x][y]);
  107.         }
  108.     };
  109.  
  110.     ring_iterator begin()
  111.     {
  112.         return ring_iterator(this, ring, ring);
  113.     }
  114.  
  115.     ring_iterator end()
  116.     {
  117.         return begin();
  118.     }
  119.  
  120.     int size() const
  121.     {
  122.         return 2*(rows+cols -2) - 4 * ring;
  123.     }
  124. };
  125.  
  126. using Matrix = std::vector<std::vector<int>>;
  127.  
  128. void rotate_mat (Matrix &mat, int r){
  129.     auto n_rings = std::min(mat.size(),mat[0].size())/2; // Number of rings
  130.     for(auto ring_i=0; ring_i<n_rings; ++ring_i){
  131.         RingView view(mat,ring_i);
  132.         int r_modulo = (r % view.size() + view.size()) % view.size();
  133.         auto next_location = view.begin();
  134.         std::advance(next_location, r_modulo);
  135.         std::rotate(view.begin(),next_location,view.end());
  136.     }
  137. }
  138.  
  139. void print_matrix(Matrix &mat){
  140.     for (auto& i : mat){
  141.         for (auto& j : i) {
  142.             std::cout << j << " ";
  143.         }
  144.         std::cout << "\n";
  145.     }
  146.     std::cout << "\n";
  147. };
  148.  
  149. int main() {
  150.     std::vector<std::vector<int>> data = { {1,2,3,4}, {5,6,7,8}, {9,10,11,12}, {13,14,15,16}, {17, 18, 19, 20} };
  151.     print_matrix(data);
  152.     rotate_mat(data, -2);
  153.     print_matrix(data);
  154.     return 0;
  155. }
Success #stdin #stdout 0s 15248KB
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Standard input is empty
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1 2 3 4 
5 6 7 8 
9 10 11 12 
13 14 15 16 
17 18 19 20 

3 4 8 12 
2 14 10 16 
1 15 6 20 
5 11 7 19 
9 13 17 18
https://ideone.com/I3vg5v
language:
C++14 (clang 8.0)
created:
6 years ago
visibility:
public

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