【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)

 

 

class Solution {
public:
    void rotate(vector<vector<int> > &matrix) {
       
        int n=matrix.size();
        int leftUp=0;
        int rightBottom=n-1;
        while(rightBottom>leftUp)
        {
            int n0=rightBottom+leftUp;
            for(int i=leftUp;i<rightBottom;i++)
            {
                int tmp=matrix[leftUp][i];
                matrix[leftUp][i]=matrix[n0-i][leftUp];
                matrix[n0-i][leftUp]=matrix[n0-leftUp][n0-i];
                matrix[n0-leftUp][n0-i]=matrix[i][n0-leftUp];
                matrix[i][n0-leftUp]=tmp;
 
            }
           
            leftUp++;rightBottom--;
        }
    }
};