[leetcode] Rotate Image

Rotate Image

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?

 

分析：rotate之后：

        matrix[i][j] = matrix[n-1-j][i];
        matrix[n-1-j][i] = matrix[n-1-i][n-1-j];
        matrix[n-1-i][n-1-j] = matrix[j][n-1-i];
        matrix[j][n-1-i] =matrix[i][j];

 

class Solution
{
public:
  void rotate(vector<vector<int> > &matrix)
  {
    if(matrix.empty()) return;

    int n = matrix.size();

    for(int i=0; i<=(n-1)/2; i++)
    {
      for(int j = i; j<n-i-1; j++)
      {
        int temp = matrix[i][j];
        matrix[i][j] = matrix[n-1-j][i];
        matrix[n-1-j][i] = matrix[n-1-i][n-1-j];
        matrix[n-1-i][n-1-j] = matrix[j][n-1-i];
        matrix[j][n-1-i] = temp;
      }
    }
  }
};