矩阵从1开始，判断是否可以完全覆盖：g.Dance(0)
const int maxnode = 100010;
const int MaxM = 1010;
const int MaxN = 1010;
struct DLX { //四向链表
int n, m, size; //n行，m列；元素上下左右对应指针
int U[maxnode], D[maxnode], L[maxnode], R[maxnode], Row[maxnode], Col[maxnode];
int H[MaxN], S[MaxM]; //S为每列元素个数， H指向每行末尾元素
int ansd, ans[MaxN]; //ansd为解的行数
void init(int _n, int _m) { //初始化
n = _n;
m = _m;
for (int i = 0; i <= m; i++) {
S[i] = 0;
U[i] = D[i] = i;
L[i] = i - 1;
R[i] = i + 1;
}
R[m] = 0; L[0] = m;
size = m;
for (int i = 1; i <= n; i++)
H[i] = -1;
}
void Link(int r, int c) { //添加
++S[Col[++size] = c];
Row[size] = r;
D[size] = D[c];
U[D[c]] = size;
U[size] = c;
D[c] = size;
if (H[r] < 0)H[r] = L[size] = R[size] = size;
else {
R[size] = R[H[r]];
L[R[H[r]]] = size;
L[size] = H[r];
R[H[r]] = size;
}
}
void remove(int c) { //删除一列
L[R[c]] = L[c]; R[L[c]] = R[c];
for (int i = D[c]; i != c; i = D[i])
for (int j = R[i]; j != i; j = R[j]) {
U[D[j]] = U[j];
D[U[j]] = D[j];
--S[Col[j]];
}
}
void resume(int c) { //恢复一列
for (int i = U[c]; i != c; i = U[i])
for (int j = L[i]; j != i; j = L[j])
++S[Col[U[D[j]] = D[U[j]] = j]];
L[R[c]] = R[L[c]] = c;
}
bool Dance(int d) { //d为递归深度
if (R[0] == 0) {
ansd = d;
return true;
}
int c = R[0];
for (int i = R[0]; i != 0; i = R[i])
if (S[i] < S[c])
c = i;
remove(c);
for (int i = D[c]; i != c; i = D[i]) {
ans[d] = Row[i];
for (int j = R[i]; j != i; j = R[j]) remove(Col[j]);
if (Dance(d + 1))return true;
for (int j = L[i]; j != i; j = L[j]) resume(Col[j]);
}
resume(c);
return false;
}
}g;
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