solution.java

public class Main {
    public static int N = 10;
    public static int e[][] = new int[N][N];// 存储二极管相邻的信息
    public static int f[] = new int[N];// 并查集
    public static int ans = 0;
    public static boolean st[] = new boolean[N];// true表示发光

    public static void init() {
        e[1][2] = e[1][6] = 1;// 表示相邻
        e[2][1] = e[2][7] = e[2][3] = 1;
        e[3][2] = e[3][7] = e[3][4] = 1;
        e[4][3] = e[4][5] = 1;
        e[5][7] = e[5][6] = e[5][4] = 1;
        e[6][5] = e[6][7] = e[6][1] = 1;
        e[7][2] = e[7][3] = e[7][5] = e[7][6] = 1;
    }

    public static int find(int u) {
        if (f[u] == u)
            return u;
        f[u] = find(f[u]);
        return f[u];
    }

    public static void dfs(int d) {// 1-7
        if (d > 7) {
            // 终止条件
            for (int i = 1; i <= 7; i++) {// 并查集初始化
                f[i] = i;
            }
            for (int i = 1; i <= 7; i++) {
                for (int j = 1; j <= 7; j++) {
                    if (e[i][j] == 1 && st[i] == true && st[j] == true) {// 把所有发光且相邻的二极管合并
                        int fx = find(i), fy = find(j);
                        if (fx != fy) {
                            f[fx] = fy;// 合并
                        }
                    }

                }
            }
            int k = 0;// 表示产生的集合的个数
            for (int i = 1; i <= 7; i++) {
                if (st[i] && f[i] == i)
                    k++;
            }
            if (k == 1)
                ans++;// 只产生一个集合，说明所有的发光二极管是连成一片的
            return;
        }

        st[d] = true;
        dfs(d + 1);
        st[d] = false;
        dfs(d + 1);
    }

    public static void main(String[] args) {
        init();
        dfs(1);
        System.out.println(ans);
    }

}