[LeetCode]--48. 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?

本地使得二维矩阵，旋转90角度。

通过实际数据分析，通过两个步骤的元素交换可实现目标：

按照主对角线，将对称元素交换
按照列，将对称列元素全部交换
即可达到，使得二维矩阵，本地旋转90个角度。

public void rotate(int[][] matrix) {
        if (matrix.length == 0)
            return;
        int n = matrix.length;
        //主对角线元素交换
        for (int i = 0; i < n; i++)
            for (int j = 0; j < i; j++) {
                int temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        //对称列元素交换
        for (int i = 0, j = n - 1; i < j; i++, j--)
            for (int k = 0; k < n; k++) {
                int temp = matrix[k][i];
                matrix[k][i] = matrix[k][j];
                matrix[k][j] = temp;
            }
    }