Exact cover（HUST1017)

/************************************************
Author        :xiecong
Created Time  :2015/9/20 22:55:25
File Name     :D:\acm\2015\专题学习\DLX\HUST1017.cpp
************************************************ */
#include <cstdio>
#include <iostream>
#include <cstring>
using namespace std;
typedef long long ll;
struct DLX{
const static int maxn =100000+7;
const static int maxnode = 100000+7;
int L[maxn],R[maxn],U[maxn],D[maxn];
int ans[maxn],size,cnt,row[maxn],col[maxn],S[maxn],H[maxn];
/*add data here*/
void del(int c){
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 add(int c){
R[L[c]]=L[R[c]]=c;
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]];
}
void init(int m){
for(int i=0;i<=m;i++){
S[i]=0;
L[i]=i-1;
R[i]=i+1;
U[i]=D[i]=i;
}
L[0]=m;R[m]=0;
size=m+1;
memset(H,-1,sizeof(H));
}
void link(int x,int y){
++S[col[size]=y];
row[size]=x;
D[size]=D[y];
U[D[y]]=size;
U[size]=y;
D[y]=size;
if(H[x]<0)H[x]=L[size]=R[size]=size;
else {
R[size]=R[H[x]];
L[R[H[x]]]=size;
L[size]=H[x];
R[H[x]]=size;
}
size++;
}
bool dfs(int k){
if(!R[0]){
cnt=k;
return 1;
}
int c=R[0];for(int i=R[0];i;i=R[i])if(S[c]>S[i])c=i;
del(c);
for(int i=D[c];i!=c;i=D[i]){
for(int j=R[i];j!=i;j=R[j])del(col[j]);
ans[k]=row[i];
if(dfs(k+1))return true;
for(int j=L[i];j!=i;j=L[j])add(col[j]);
}
add(c);
return 0;
}
void showpath(){
printf("%d",cnt);
for(int i=0;i<cnt;i++)
printf(" %d",ans[i]);
putchar('\n');
}
}dlx;
int n,m;
int main()
{
while(scanf("%d%d",&n,&m)==2){
dlx.init(m);
for(int i=1;i<=n;i++){
int mm, k ;
scanf("%d",&mm);
for(int j=1;j<=mm;j++){
scanf("%d",&k);
dlx.link(i,k);
}
}
if(dlx.dfs(0)) dlx.showpath();
else puts("NO");
}
return 0;
}