LeetCode - 48. Rotate Image

问题

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?

代码

class Solution {
public:
    //我的方法：比较费空间
    void rotate(vector<vector<int>>& matrix) {
        vector<vector<int> > temp = matrix;
        matrix.clear();
        vector<int> vec;
        for(int i=0; i//因为是n*n，所以temp.size() == temp[0].size()
        {
            for(int j=temp.size()-1; j>=0; j--)
                vec.push_back(temp[j][i]);

            matrix.push_back(vec);
            vec.clear();        //切记clear
        }
    }

    //高分参考答案，节省空间
    /*
   * clockwise rotate
   * first reverse up to down, then swap the symmetry 
   * 1 2 3     7 8 9     7 4 1
   * 4 5 6  => 4 5 6  => 8 5 2
   * 7 8 9     1 2 3     9 6 3
  */
  void rotate(vector<vector<int> > &matrix) {
      reverse(matrix.begin(), matrix.end());
      for (int i = 0; i < matrix.size(); ++i) {
          for (int j = i + 1; j < matrix[i].size(); ++j)
              swap(matrix[i][j], matrix[j][i]);
      }
  }

  /*
   * anticlockwise rotate  //逆时针旋转时
   * first reverse left to right, then swap the symmetry
   * 1 2 3     3 2 1     3 6 9
   * 4 5 6  => 6 5 4  => 2 5 8
   * 7 8 9     9 8 7     1 4 7
  */
  void anti_rotate(vector<vector<int> > &matrix) {
      for (auto vi : matrix) reverse(vi.begin(), vi.end());
      for (int i = 0; i < matrix.size(); ++i) {
          for (int j = i + 1; j < matrix[i].size(); ++j)
              swap(matrix[i][j], matrix[j][i]);
      }
}