N x N 的矩阵，顺时针旋转

第一种方法：

先打印外圈，再打印内圈

public class RotateMatrix1 {

    public static void rotate(int[][] matrix) {
        int tR = 0;
        int tC = 0;
        int bR = matrix.length - 1;
        int bC = matrix[0].length - 1;
        while (tR < bR) {
            rotateEdge(matrix, tR++, tC++, bR--, bC--);
        }
    }

    public static void rotateEdge(int[][] m, int a, int b, int c, int d) {
        int times = d - b; 
        int tmp = 0;
        for (int i = 0; i != times; i++) {
            tmp = m[a][b + i];
            m[a][b + i] = m[c - i][b];
            m[c - i][b] = m[c][d - i];
            m[c][d - i] = m[a + i][d];
            m[a + i][d] = tmp;
        }
    }

    public static void printMatrix(int[][] matrix) {
        for (int i = 0; i != matrix.length; i++) {
            for (int j = 0; j != matrix[0].length; j++) {
                System.out.print(matrix[i][j] + " ");
            }
            System.out.println();
        }
    }

    public static void main(String[] args) {
        int[][] matrix = { { 1, 2, 3, 4 }, 
                           { 5, 6, 7, 8 },
                           { 9, 10, 11, 12 },
                           { 13, 14, 15, 16 } };
        printMatrix(matrix);
        rotate(matrix);
        System.out.println("********************");
        printMatrix(matrix);

    }
}

第二种方法：

按照对角线交换后，再交换列

public class RotateMatrix2 {

    //主对角线不变，主对角线对称的点互换位置
    public static void  symmetry(int[][] matrix) {
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < i; j++) {
                int temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
    }

    //总体的效果是交换整列，假如总共有4列，那么第0列和第3列交换，第1列和第2列交换，
    //实现过程是可以一行一行交，第0行交换完了，再交换下一行
    public static void swapCol(int [][] matrix) {
        for(int i = 0; i<matrix.length; i++) {
            for(int j = 0; j<matrix.length/2; j++) {
                 int temp = matrix[i][j];
                 matrix[i][j] = matrix[i][matrix[0].length - 1 - j];
                 matrix[i][matrix[0].length - 1 - j] = temp;
            }
        }
    }
    
    public static void main(String[] args) {
        int[][] matrix = { { 1, 2, 3, 4 }, 
                           { 5, 6, 7, 8 },
                           { 9, 10, 11, 12 },
                           { 13, 14, 15, 16 } };
        printMatrix(matrix);
        symmetry(matrix);
        System.out.println("********************");
        printMatrix(matrix);
        swapCol(matrix);
        System.out.println("********************");
        printMatrix(matrix);
    }
    
    public static void printMatrix(int[][] matrix) {
        for (int i = 0; i != matrix.length; i++) {
            for (int j = 0; j != matrix[0].length; j++) {
                System.out.print(matrix[i][j] + " ");
            }
            System.out.println();
        }
    }
}