Rotate Image

You are given an n x n 2D matrix representing an image. Rotate the image by 90 degrees (clockwise). Follow up: Could you do this in-place?

Solution

public class Solution {
    public void rotate(int[][] matrix) {
        rotate(matrix, matrix.length, 0, matrix.length - 2);
    }

    public void rotate(int[][] matrix, int n, int level, int maxJ) {
        if (maxJ < 0) {
            return;
        } else {

            int i = level;
            for (int j = 0; j <= maxJ; j++) {
                int tmp = matrix[i][i + j];
                matrix[i][i + j] = matrix[n - i - j - 1][i];
                matrix[n - i - j - 1][i] = matrix[n - i - 1][n - i - j - 1];
                matrix[n - i - 1][n - i - j - 1] = matrix[i + j][n - i - 1];
                matrix[i + j][n - i - 1] = tmp;
            }

            rotate(matrix, n, level + 1, maxJ - 2);
        }
    }
}