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  1. Prepare
  2. Algorithms
  3. Implementation
  4. Matrix Layer Rotation
  5. Discussions

Matrix Layer Rotation

  • anarod_val25
     + 0 comments

    They called me a mad man. Single pass, 1 nested loop, let's goooooooooo!

    So, what we are doing, since we already have the matrix, is calculating the location of the number from the original matrix that should fall on the position we are currently printing. So, instead of transforming the matrix, we are kind of going in the oposite directioin and figuring out what number would be where in the final matrix rather than transforming it.

    (The amount of times those ifs were tweaked is not up for discussion.)

    Also, do beware, this is not a pretty sight. 

    void matrixRotation(vector<vector<int>> matrix, int r) {
    int row = matrix.size(), col = matrix[0].size();
    
    for (int i = 0; i < row; i++) {
        for (int j = 0; j < col; j++) {
            
            int layer = min({i, j, row-1-i, col-1-j});
            
            int top = layer, left = layer;
            int bottom = row-1-layer, right = col-1-layer;
            
            int perimeter = 2 * ((bottom-top) + (right-left));
            
            int idx = 0;
            if (i == top){ 
                idx = j-left;
            }else if (j == right){
                idx = (right-left) + (i-top);
            }else if (i == bottom){ 
                idx = (right-left) + (bottom-top) + (right-j);
            }else{ 
                idx = (right-left) + (bottom-top) + (right-left) + (bottom-i);
            }
            
            int newIdx = (idx + r) % perimeter;
            
            int x, y;
            if (newIdx < (right-left)){ 
                x = top; 
                y = left + newIdx; 
            }else if (newIdx < (right-left) + (bottom-top)){ 
                x = top + (newIdx - (right-left)); 
                y = right; 
            }else if (newIdx < (right-left)*2 + (bottom-top)){ 
                x = bottom; 
                y = right - (newIdx - ((right-left)+(bottom-top))); 
            }else{ 
                x = bottom - (newIdx - ((right-left)*2 + (bottom-top))); 
                y = left; 
            }
            
            cout << matrix[x][y] << " ";
        }
        cout << endl;
    }
}