48. Rotate Image

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]
]
首先我想说，leetcode上的大神真实他妈的宇宙无敌超级他妈的几把厉害，哦也可能是我太菜
先交换行，再转置（两个可以交换顺序），就完成90度旋转了，真他妈的厉害。把我这个菜逼看的一愣一愣的

class Solution {
    public void rotate(int[][] matrix) {
        /*1. 先交换行（先转置再交换列也行，但交换列对java不友好）
          2. 再转置
        */
        if(matrix.length<=1) return;
         int n = matrix.length;
        /*  1,2,3
            4,5,6
            7,8,9
        */
        for(int i=0;i<n/2;i++){
            int[] temp = matrix[i];
            matrix[i] = matrix[n-1-i];
            matrix[n-1-i] = temp;
        }
        /*  7,8,9
            4,5,6
            1,2,3
        */
        
        for(int i=0;i<n;i++){
            for(int j=i;j<n;j++){
                int temp =  matrix[j][i];
                matrix[j][i] = matrix[i][j];
                matrix[i][j] = temp;

            }
        }
        /*  7,4,1
            8,5,2
            9,6,3
        */  
    }