RotateImage.java

/**
 * You are given an n x n 2D matrix representing an image.
 * <p>
 * Rotate the image by 90 degrees (clockwise).
 * <p>
 * Note:
 * 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.
 * <p>
 * Example 1:
 * <p>
 * Given input matrix =
 * [
 * [1,2,3],
 * [4,5,6],
 * [7,8,9]
 * ],
 * <p>
 * rotate the input matrix in-place such that it becomes:
 * [
 * [7,4,1],
 * [8,5,2],
 * [9,6,3]
 * ]
 * Example 2:
 * <p>
 * Given input matrix =
 * [
 * [ 5, 1, 9,11],
 * [ 2, 4, 8,10],
 * [13, 3, 6, 7],
 * [15,14,12,16]
 * ],
 * <p>
 * rotate the input matrix in-place such that it becomes:
 * [
 * [15,13, 2, 5],
 * [14, 3, 4, 1],
 * [12, 6, 8, 9],
 * [16, 7,10,11]
 * ]
 * <p>
 * Accepted.
 */
public class RotateImage {

    public void rotate(int[][] matrix) {
        // Reverse
        for (int i = 0; i < matrix.length / 2; i++) {
            int j = matrix.length - 1 - i;
            int[] cache = matrix[i];
            matrix[i] = matrix[j];
            matrix[j] = cache;
        }
        // Transpose
        for (int i = 0; i < matrix.length; i++) {
            for (int j = i + 1; j < matrix.length; j++) {
                int cache = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = cache;
            }
        }
    }

}