48-Rotate Image

【题目】

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?

【analyze】

1.先对角线旋转

2.再左右对调

【算法】

public class Solution {
    public void rotate(int[][] matrix) {
        int r=matrix.length;
        int c=matrix[0].length;
        //按主对角线翻转矩阵
        for(int i=0;i<r-1;i++) {
            for(int j=1+i;j<c;j++) {
                int temp=matrix[i][j];
                matrix[i][j]=matrix[j][i];
                matrix[j][i]=temp;
            }
        }
        //左右对调
        for(int i=0;i<r;i++) {
            for(int j=0;j<c/2;j++) {
                int temp=matrix[i][j];
                matrix[i][j]=matrix[i][c-1-j];
                matrix[i][c-1-j]=temp;
            }
        }
    }
}