舞蹈链模板 Dancing Links

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;