Android Unlock Patterns

public class Solution {
    private boolean[][] visited = new boolean[3][3];
    private int m;
    private int n;
    public int numberOfPatterns(int m, int n) {
        if (n == 0 || m > n) {
            return 0;
        }
        int result = 0;
        this.m = m;
        this.n = n;
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                visited[i][j] = true;
                result += getPattern(i, j, 1);
                visited[i][j] = false;
            }
        }
        return result;
    }

    private int getPattern(int x, int y, int level) {
        if (level > n) {
            return 0;
        }

        int result = level >= m ? 1 : 0;
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                if (visited[i][j] ||
                x == i && Math.abs(y - j) == 2 && !visited[i][1] ||
                y == j && Math.abs(x - i) == 2 && !visited[1][j] ||
                Math.abs(x - i) == 2 && Math.abs(y - j) == 2 && !visited[1][1]) {
                    continue;
                }
                visited[i][j] = true;
                result += getPattern(i, j, level + 1);
                visited[i][j] = false;
            }
        }
        return result;
    }
}

1. 3x3 pattern board. Do not mess it up.

2. pattern counting start from 1, not 0