旋转矩阵

 * @lc app=leetcode id=48 lang=cpp
 *
 * [48] Rotate Image
 *
 * https://leetcode.com/problems/rotate-image/description/
 *
 * algorithms
 * Medium (45.23%)
 * Total Accepted:    204.8K
 * Total Submissions: 452.8K
 * Testcase Example:  '[[1,2,3],[4,5,6],[7,8,9]]'
 *
 * You are given an n x n 2D matrix representing an image.
 * 
 * Rotate the image by 90 degrees (clockwise).
 * 
 * Note:
 * 
 * You have to rotate the image in-place, which means you have to modify the
 * input 2D matrix directly. DO NOT allocate another 2D matrix and do the
 * rotation.
 * 
 * Example 1:
 * 
 * 
 * Given input matrix = 
 * [
 * ⁠ [1,2,3],
 * ⁠ [4,5,6],
 * ⁠ [7,8,9]
 * ],
 * 
 * rotate the input matrix in-place such that it becomes:
 * [
 * ⁠ [7,4,1],
 * ⁠ [8,5,2],
 * ⁠ [9,6,3]
 * ]
 * 
 * 
 * Example 2:
 * 
 * 
 * Given input matrix =
 * [
 * ⁠ [ 5, 1, 9,11],
 * ⁠ [ 2, 4, 8,10],
 * ⁠ [13, 3, 6, 7],
 * ⁠ [15,14,12,16]
 * ], 
 * 
 * rotate the input matrix in-place such that it becomes:
 * [
 * ⁠ [15,13, 2, 5],
 * ⁠ [14, 3, 4, 1],
 * ⁠ [12, 6, 8, 9],
 * ⁠ [16, 7,10,11]
 * ]
 * 
 * 
 */
class  {
public:
    void swap(int &a,int &b)
    {
        int t=a;
        a=b;
        b=t;
    }
    void rotate(vector<vector<int>>& matrix) {
        int n=matrix[0].size();
       /* for(int i=0;i<n/2;i++)
        {
            for(int j=i;j<n-1-i;j++)
            {
                int temp=matrix[j][n-i-1];
                matrix[j][n-i-1]=matrix[i][j];
                matrix[i][j]=matrix[n-j-1][i];
                matrix[n-j-1][i] = matrix[n-i-1][n-j-1];
                matrix[n-i-1][n-j-1] = temp;
            }
          
        }*/
        for(int i=0;i<n;i++)//对角线对折
        {
            for(int j=i;j<n;j++)
            {
                swap(matrix[i][j],matrix[j][i]);
            }
        }//for

        for(int i=0;i<n;i++)//对中线对折
        {
            for(int j=0;j<n/2;j++)
            {
                swap(matrix[i][j],matrix[i][n-1-j]);
            }
        }//for
        
    }
};