1. /**
    2.  * 48. Rotate Image
    3.  * <p>
    4.  * You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).
    5.  * <p>
    6.  * You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.
    7.  * <p>
    8.  * <p>
    9.  * <p>
    10.  * Example 1:
    11.  * <p>
    12.  * <p>
    13.  * Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
    14.  * Output: [[7,4,1],[8,5,2],[9,6,3]]
    15.  * Example 2:
    16.  * <p>
    17.  * <p>
    18.  * Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]
    19.  * Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]
    20.  * Example 3:
    21.  * <p>
    22.  * Input: matrix = [[1]]
    23.  * Output: [[1]]
    24.  * Example 4:
    25.  * <p>
    26.  * Input: matrix = [[1,2],[3,4]]
    27.  * Output: [[3,1],[4,2]]
    28.  * <p>
    29.  * <p>
    30.  * Constraints:
    31.  * <p>
    32.  * matrix.length == n
    33.  * matrix[i].length == n
    34.  * 1 <= n <= 20
    35.  * -1000 <= matrix[i][j] <= 1000
    36.  */
    37. public class Lesson48 {
    39.     public static void main(String[] args) {
    40.         int len = (int) (Math.random() * 10);
    41.         int[][] matrix = new int[len][len];
    42.         for (int i = 0; i < len; i++) {
    43.             for (int j = 0; j < len; j++) {
    44.                 matrix[i][j] = (int) (Math.random() * 1000);
    45.             }
    46.         }
    47.         printMatrix(matrix);
    48.         new Solution().rotate(matrix);
    49.         printMatrix(matrix);
    51.     }
    53.     private static void printMatrix(int[][] matrix) {
    54.         int n = matrix.length;
    55.         StringBuilder stringBuilder = new StringBuilder();
    56.         stringBuilder.append("[");
    57.         for (int i = 0; i < n; i++) {
    58.             stringBuilder.append("[");
    59.             for (int j = 0; j < n; j++) {
    60.                 stringBuilder.append(matrix[i][j]).append(j == n -1 ? "" : ",");
    61.             }
    62.             stringBuilder.append(i == n -1 ? "]" : "],").append("\n");
    63.         }
    64.         stringBuilder.append("]");
    65.         Util.println(stringBuilder);
    66.     }
    68.     static class Solution {
    70.         public void rotate(int[][] matrix) {
    71.             int n;
    72.             if (matrix == null || (n = matrix.length) == 0 || matrix[0].length != n) {
    73.                 return ;
    74.             }
    76.             int[] tempArr = new int[4];
    78.             for (int end = n, start = 0; end > 0 && end - start > 1; end--,start = n - end) {
    79.                 int last = end - 1;
    80.                 for (int i = start; i < end - 1; i++) {
    81.                     int offset = (i - start);
    82.                     tempArr[0] = matrix[start][i];
    83.                     tempArr[1] = matrix[i][last];
    84.                     tempArr[2] = matrix[last][last - offset];
    85.                     tempArr[3] = matrix[last - offset][start];
    87.                     matrix[start][i] = tempArr[3];
    88.                     matrix[i][last] = tempArr[0];
    89.                     matrix[last][last - offset] = tempArr[1];
    90.                     matrix[last - offset][start] = tempArr[2];
    91.                 }
    92.             }
    94.         }
    96.     }
    98. }