HUST 1017 Exact Cover（舞蹈链模板）

题意就不多说了，标准的测舞蹈链的题目，花了一下午看了很多博客，终于
看懂了原理，理解之后其实挺清晰地，本来想去看论文原文的，后来还是看
了中文的翻译版，英文太难受了。
推荐两个博客 http://www.cnblogs.com/grenet/p/3145800.html http://blog.csdn.net/yysdsyl/article/details/4266876
这两个讲的挺清晰的
论文中文版 http://io.sqybi.com/dlxcn/ 至于里面有一个优化的措施我个人觉得没啥道理啊- -
我加了反而变慢了
本来我的代码跑的本来就慢，可能是用了STL的缘故。
不过换了一个版本，也就是现在的版本，挺快的

//
//  Created by  CQU_CST_WuErli
//  Copyright (c) 2016 CQU_CST_WuErli. All rights reserved.
//
#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <map>
#include <queue>
#include <stack>
#include <set>
#include <algorithm>
#include <sstream>
#define CLR(x) memset(x,0,sizeof(x))
#define OFF(x) memset(x,-1,sizeof(x))
#define MEM(x,a) memset((x),(a),sizeof(x))
#define BUG cout << "I am here" << endl
#define lookln(x) cout << #x << "=" << x << endl
#define SI(a) scanf("%d",&a)
#define SII(a,b) scanf("%d%d",&a,&b)
#define SIII(a,b,c) scanf("%d%d%d",&a,&b,&c)
#define rep(flag,start,end) for(int flag=start;flag<=end;flag++)
#define Rep(flag,start,end) for(int flag=start;flag>=end;flag--)
#define Lson l,mid,rt<<1
#define Rson mid+1,r,rt<<1|1
#define Root 1,n,1
#define BigInteger bign
const int MAX_L=2005;// For BigInteger
const int INF_INT=0x3f3f3f3f;
const long long INF_LL=0x7fffffff;
const int MOD=1e9+7;
const double eps=1e-9;
const double pi=acos(-1);
typedef long long  ll;
using namespace std;

const int N=1010;

int n,m;

struct Node {
int right,left,down,up;
int size;
int x,y;
};

struct DLX {
const static int maxn=1000010; // 节点总数
Node p[maxn];
int size;                       // 节点标记
int head[maxn];                 // 行标指针
int vis[maxn];
stack<int> Ans;
int ans;
void init(int m) {
for (int i=0;i<=m;i++) {
p[i].up=p[i].down=i;
p[i].left=i-1;p[i].right=i+1;
p[i].size=0;
}
p[0].left=m;p[m].right=0;
OFF(head);
size=m+1;
ans=-1;
while (Ans.size()) Ans.pop();
}
void link(int row,int col) {
p[size].x=row;p[size].y=col;p[col].size++;
p[size].up=p[col].up;p[p[col].up].down=size;
p[col].up=size;p[size].down=col;
if (head[row]<0) head[row]=p[size].left=p[size].right=size;
else {
p[size].right=p[head[row]].right;p[p[head[row]].right].left=size;
p[size].left=head[row];p[head[row]].right=size;
}
size++;
}
// exact cover
void remove(int c) {
p[p[c].right].left=p[c].left;
p[p[c].left].right=p[c].right;
for (int i=p[c].down;i!=c;i=p[i].down) {
for (int j=p[i].right;j!=i;j=p[j].right) {
p[p[j].down].up=p[j].up;
p[p[j].up].down=p[j].down;
p[p[j].y].size--;
}
}
}
void resume(int c) {
p[p[c].left].right=c;
p[p[c].right].left=c;
for (int i=p[c].up;i!=c;i=p[i].up) {
for (int j=p[i].left;j!=i;j=p[j].left) {
p[p[j].down].up=j;
p[p[j].up].down=j;
p[p[j].y].size++;
}
}

}
bool dfs(int cnt) {
if (ans!=-1) return true;
if (p[0].right==0) {
ans=cnt;
return true;
}
int c=0;
int Min=INF_INT;
for (int i=p[0].right;i!=0;i=p[i].right)
if (Min>p[i].size) Min=p[i].size,c=i;
remove(c);
for (int i=p[c].down;i!=c;i=p[i].down) {
Ans.push(p[i].x);
for (int j=p[i].right;j!=i;j=p[j].right) {
remove(p[j].y);
}
if (dfs(cnt+1)) return true;
for (int j=p[i].left;j!=i;j=p[j].left) {
resume(p[j].y);
}
Ans.pop();
}
resume(c);
return false;
}
// exact cover ends;
// multiple cover
void del(int c) {
for (int i=p[c].down;i!=c;i=p[i].down) {
p[p[i].right].left=p[i].left;
p[p[i].left].right=p[i].right;
}
}
void rec(int c) {
for (int i=p[c].up;i!=c;i=p[i].up) {
p[p[i].right].left=i;
p[p[i].left].right=i;
}
}
int h() {
int ret=0;
CLR(vis);
for (int i=p[0].right;i!=0;i=p[i].right) if (!vis[i]) {
ret++;vis[i]=1;
for (int j=p[i].down;j!=i;j=p[j].down)
for (int k=p[j].right;k!=j;k=p[k].right)
vis[p[k].y]=1;
}
return ret;
}
void DFS(int cnt) {
if (p[0].right==0) ans=min(ans,cnt);
else if (h()+cnt<ans) {
int c=0;
int Min=INF_INT;
for (int i=p[c].right;i!=0;i=p[i].right){
if (p[i].size<Min) Min=p[i].size,c=i;
}
// lookln(c);
for (int i=p[c].down;i!=c;i=p[i].down) {
del(i);
for (int j=p[i].right;j!=i;j=p[j].right) del(j);
DFS(cnt+1);
// BUG;
for (int j=p[i].left;j!=i;j=p[j].left) rec(j);
rec(i);
}
}
return;
}
// multiple cover ends;
}dlx;
/*
0 1  2  3  4  5  6  7
8  0  0  9  0  0  10
11 0  0  12 0  0  0
0  0  0  13 14 0  15
0  0  16 0  17 18 0
0  19 20 0  0  21 22
0  23 0  0  0  0  24
*/

int main(int argc, char const *argv[]) {
#ifdef LOCAL
freopen("C:\\Users\\john\\Desktop\\in.txt","r",stdin);
// freopen("C:\\Users\\john\\Desktop\\out.txt","w",stdout);
#endif
// BUG;
while(SII(n,m)==2) {
dlx.init(m);
for (int i=1;i<=n;i++){
int x;SI(x);
while (x--) {
int tmp;SI(tmp);
dlx.link(i,tmp);
}
}
if (dlx.dfs(0)) {
cout << dlx.ans;
while (dlx.Ans.size()) {
cout << ' ' << dlx.Ans.top();
dlx.Ans.pop();
}
cout << endl;
}
else puts("NO");
}
return 0;
}