cci-Q1.6 矩形90度旋转

来源：互联网发布：北京雾霾知乎编辑：程序博客网时间：2024/05/08 22:43

原文：

Given an image represented by an NxN matrix, where each pixel in the image is 4 bytes, write a method to rotate the image by 90 degrees. Can you do this in place?

译文：

一张图像表示成NxN的矩阵，图像中每个像素是4个字节，写一个函数把图像旋转90度。你能原地进行操作吗？(即不开辟额外的存储空间)

N*N矩形，旋转90度，直观来看就是最外圈进行旋转，一层一层往里再进行旋转。

 public static int[][] rotate(int[][] matrix, int n) {        for (int layer = 0; layer < n / 2; layer++) {            int first = layer;            int last = n - first - 1;            for (int i = first; i < last; i++) {                int offset = i - first;                //Save top                int top = matrix[first][i];                // left->top                matrix[first][i] = matrix[last - offset][first];                //bottom->left                matrix[last - offset][first] = matrix[last][last - offset];                //right->bottom                matrix[last][last - offset] = matrix[i][last];                //top->right                matrix[i][last] = top;            }        }        return matrix;    }

junit testcase

    @Test    public void testRotate() {        System.out.println("rotate");        int[][] test = {{1, 2}, {3, 4}};        int[][] expected = {{3, 1}, {4, 2}};        assertArrayEquals(expected, q1_6.rotate(test, 2));        int[][] test1 = {{1}};        int[][] expected1 = {{1}};        assertArrayEquals(expected1, q1_6.rotate(test1, 1));        int[][] test2 = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}, {13, 14, 15, 16}};        int[][] expected2 = {{13, 9, 5, 1}, {14, 10, 6, 2}, {15, 11, 7, 3}, {16, 12, 8, 4}};        assertArrayEquals(expected2, q1_6.rotate(test2, 4));        int[][] test3 = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};        int[][] expected3 = {{7, 4, 1}, {8, 5, 2}, {9, 6, 3}};        assertArrayEquals(expected3, q1_6.rotate(test3, 3));    }