【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?

 

 

假设旋转的时候，左上角元素为(l,l)，右下角元素为(r,r)

则旋转的时候

(l,l+1)=(r-1,l) 最上面一排 

(r-1,l)=(r,r-1)左边一排

(r,r-1)=(l+1,r)下面一排

(l+1,r)=(l,l+1)右边一排

 

可以找到规律

(i,j)--->(r+l-j,i)

 

 

 1 class Solution {

 2 public:

 3     void rotate(vector<vector<int> > &matrix) {

 4        

 5         int n=matrix.size();

 6         int leftUp=0;

 7         int rightBottom=n-1;

 8         while(rightBottom>leftUp)

 9         {

10             int n0=rightBottom+leftUp;

11             for(int i=leftUp;i<rightBottom;i++)

12             {

13                 int tmp=matrix[leftUp][i];

14                 matrix[leftUp][i]=matrix[n0-i][leftUp];

15                 matrix[n0-i][leftUp]=matrix[n0-leftUp][n0-i];

16                 matrix[n0-leftUp][n0-i]=matrix[i][n0-leftUp];

17                 matrix[i][n0-leftUp]=tmp;

18  

19             }

20            

21             leftUp++;rightBottom--;

22         }

23     }

24 };