LeetCode : 54. Spiral Matrix

class Solution {

    int[] dx = { 0, 1, 0, -1 };
    int[] dy = { 1, 0, -1, 0 };

    public List<Integer> spiralOrder(int[][] matrix) {

        List<Integer> answer = new LinkedList<>();
        boolean[][] isVisit = new boolean[matrix.length][matrix[0].length];

        return solve(answer, matrix, isVisit, 0, 0, 0);
    }

    private List<Integer> solve(List<Integer> answer, int[][] matrix, boolean[][] isVisit,
                                int dir, int x, int y) {

        isVisit[x][y] = true;
        answer.add(matrix[x][y]);

        int nx = x + dx[dir];
        int ny = y + dy[dir];

        int nextDir = getNextDirection(dir + 1);
        int nx2 = x + dx[nextDir];
        int ny2 = y + dy[nextDir];

        if (isInRange(matrix, nx, ny)
            && isVisit[nx][ny] == false) {
            solve(answer, matrix, isVisit, dir, nx, ny);

        } else if (isInRange(matrix, nx2, ny2)
                   && isVisit[nx2][ny2] == false) {
            solve(answer, matrix, isVisit, nextDir, nx2, ny2);
        }

        return answer;

    }

    private int getNextDirection(int dir) {
        return dir % 4;
    }

    private boolean isInRange(int[][] matrix, int x, int y) {
        return x >= 0 && x < matrix.length && y >= 0 && y < matrix[0].length;
    }
}