题目链接：https://leetcode.com/problems/rotate-image/
题目：
n x n
Rotate the image by 90 degrees (clockwise).
Follow up:
Could you do this in-place?
思路：
先将矩阵转置，再将矩阵按中轴线对称交换每一列。
算法：
public void rotate(int[][] matrix) {
for (int i = 0; i < matrix.length; i++) { //转置
for (int j = i; j < matrix[0].length; j++) {
int tmp = matrix[i][j];
matrix[i][j] = matrix[j][i];
matrix[j][i] = tmp;
}
}
for (int i = 0; i < matrix.length; i++) {//交换列
for (int j = 0; j < matrix[0].length / 2; j++) {
int tmp = matrix[i][j];
matrix[i][j] = matrix[i][matrix[0].length - 1 - j];
matrix[i][matrix[0].length - 1 - j] = tmp;
}
}
}