LeetCode——第48题：旋转图像

不会做转载的：原博客

题目：

给定一个 n × n 的二维矩阵表示一个图像。

将图像顺时针旋转 90 度。

说明：

你必须在原地旋转图像，这意味着你需要直接修改输入的二维矩阵。请不要使用另一个矩阵来旋转图像。

示例 1:

给定 matrix =
[
[1,2,3],
[4,5,6],
[7,8,9]
],

原地旋转输入矩阵，使其变为:
[
[7,4,1],
[8,5,2],
[9,6,3]
]

示例 2:

给定 matrix =
[
[ 5, 1, 9,11],
[ 2, 4, 8,10],
[13, 3, 6, 7],
[15,14,12,16]
],

原地旋转输入矩阵，使其变为:
[
[15,13, 2, 5],
[14, 3, 4, 1],
[12, 6, 8, 9],
[16, 7,10,11]
]

代码：

package leetCode;
/**
 * 2018.7.21
 * 旋转图像
 * @author dhc
 *
 */
public class FourtyEight {
    //直接的方法，对于当前位置，计算旋转后的新位置，然后再计算下一个新位置，第四个位置又变成当前位置了，所以这个方法每次循环换四个数字
    public static void rotate(int[][] matrix) {
        for(int i = 0;i < matrix.length/2;i++) {
            for(int j = i;j <matrix.length - 1 - i ;j++) {
                int tem = matrix[i][j];
                matrix[i][j] = matrix[matrix.length-j-1][i];
                matrix[matrix.length-j - 1][i] = matrix[matrix.length-i-1][matrix.length-j-1];
                matrix[matrix.length-i-1][matrix.length-j-1] = matrix[j][matrix.length-i-1];
                matrix[j][matrix.length-i-1] = tem;
            }
        }
    }
    //先以对角线翻转，再以行中线为轴翻转
    public static void rotate1(int[][] matrix) {
        for (int i = 0; i < matrix.length - 1; i++) {
            for (int j = 0; j < matrix.length - i; j++) {
                int tem = matrix[i][j];
                matrix[i][j] = matrix[matrix.length - 1 - j][matrix.length - 1 - i]; 
                matrix[matrix.length - 1 - j][matrix.length - 1 - i] = tem;
            }
        }
        for(int i = 0;i < matrix.length/2;i++) {
            for(int j = 0; j < matrix.length;j++) {
                int tem = matrix[i][j];
                matrix[i][j] = matrix[matrix.length - 1 - i][j];
                matrix[matrix.length-1-i][j] = tem;
            }
        }
    }
    //先求矩阵转置矩阵，在将每行数字以列中线翻转
    public static void rotate2(int[][] matrix) {
        for (int i = 0; i < matrix.length; i++) {
            for (int j = i + 1; j < matrix.length; j++) {
                int tem = matrix[i][j];
                matrix[i][j] = matrix[j][i]; 
                matrix[j][i] = tem;
            }
        }
        for(int i = 0;i < matrix.length;i++) {
            for(int j = 0; j < matrix.length/2;j++) {
                int tem = matrix[i][j];
                matrix[i][j] = matrix[i][matrix.length - 1 -j];
                matrix[i][matrix.length - 1 -j] = tem;
            }
        }
    }
    public static void main(String[] args) {
        int[][] matrix = new int[4][4]; 
        int count = 1;
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix.length; j++) {
                matrix[i][j] = count++;
            }
        }
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix.length; j++) {
                System.out.print(matrix[i][j]+" ");
            }
            System.out.println("");
        }
        System.out.println();
        rotate2(matrix);
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix.length; j++) {
                System.out.print(matrix[i][j]+" ");
            }
            System.out.println("");
        }
    }
}