【HUST】1017 Exact cover

  1 #include<cstdio>

  2 #define INF 0x7FFFFFFF

  3 #define MAXN 1000010

  4 int n, m, size;

  5 int L[MAXN], R[MAXN], U[MAXN], D[MAXN], H[MAXN];

  6 int S[MAXN], C[MAXN], X[MAXN], Q[MAXN];

  7 void Init() {

  8     int i;

  9     for (i = 0; i <= m; i++) {

 10         S[i] = 0;

 11         L[i + 1] = i;

 12         R[i] = i + 1;

 13         U[i] = D[i] = i;

 14     }

 15     R[m] = 0;

 16     size = m + 1;

 17 }

 18 void Remove(int c) {

 19     int i, j;

 20     R[L[c]] = R[c];

 21     L[R[c]] = L[c];

 22     for (i = D[c]; i != c; i = D[i]) {

 23         for (j = R[i]; j != i; j = R[j]) {

 24             D[U[j]] = D[j];

 25             U[D[j]] = U[j];

 26             S[C[j]]--;

 27         }

 28     }

 29 }

 30 void Resume(int c) {

 31     int i, j;

 32     R[L[c]] = c;

 33     L[R[c]] = c;

 34     for (i = D[c]; i != c; i = D[i]) {

 35         for (j = R[i]; j != i; j = R[j]) {

 36             U[D[j]] = j;

 37             D[U[j]] = j;

 38             S[C[j]]++;

 39         }

 40     }

 41 }

 42 void Link(int r, int c) {

 43     S[c]++;

 44     D[size] = D[c];

 45     U[size] = c;

 46     U[D[c]] = size;

 47     D[c] = size;

 48     if (H[r] < 0)

 49         H[r] = L[size] = R[size] = size;

 50     else {

 51         L[size] = H[r];

 52         R[size] = R[H[r]];

 53         L[R[H[r]]] = size;

 54         R[H[r]] = size;

 55     }

 56     C[size] = c;

 57     X[size++] = r;

 58 }

 59 bool Dance(int now) {

 60     int i, j, c, temp;

 61     if (R[0] == 0) {

 62         printf("%d", now);

 63         for (i = 0; i < now; i++)

 64             printf(" %d", X[Q[i]]);

 65         putchar('\n');

 66         return true;

 67     }

 68     for (temp = INF, i = R[0]; i; i = R[i]) {

 69         if (S[i] < temp) {

 70             c = i;

 71             temp = S[i];

 72         }

 73     }

 74     Remove(c);

 75     for (i = D[c]; i != c; i = D[i]) {

 76         Q[now] = i;

 77         for (j = R[i]; j != i; j = R[j])

 78             Remove(C[j]);

 79         if (Dance(now + 1))

 80             return true;

 81         for (j = L[i]; j != i; j = L[j])

 82             Resume(C[j]);

 83     }

 84     Resume(c);

 85     return false;

 86 }

 87 int main() {

 88     int i, j, k;

 89     while (~scanf("%d%d", &n, &m)) {

 90         Init();

 91         for (i = 1; i <= n; i++) {

 92             H[i] = -1;

 93             scanf("%d", &k);

 94             while (k--) {

 95                 scanf("%d", &j);

 96                 Link(i, j);

 97             }

 98         }

 99         if (!Dance(0))

100             puts("NO");

101     }

102     return 0;

103 }