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]]

难度： medium

题目：给定n * n的矩阵表示一张图片。顺时针90度旋转。

注意：必须原地旋转不允许申请额外的空间。

思路：90度旋转有数学规律可寻。

Runtime: 1 ms, faster than 100.00% of Java online submissions for Rotate Image.

Memory Usage: 26.4 MB, less than 46.19% of Java online submissions for Rotate Image.

class Solution {    public void rotate(int[][] matrix) {        int n = matrix.length;        int nIdx = n - 1;        for (int i = 0; i < n / 2; i++) {            int start = i;            int end = nIdx - i;            for (int j = start; j < end; j++) {                int t = matrix[nIdx - j][i];                matrix[nIdx - j][i]= matrix[end][nIdx - j];                matrix[end][nIdx - j] = matrix[j][end];                matrix[j][end] = matrix[i][j];                matrix[i][j] = t;             }        }    } }