hust 1017 DLX

#include<set>

#include<cmath>

#include<queue>

#include<cstdio>

#include<vector>

#include<string>

#include<cstdlib>

#include<cstring>

#include<iostream>

#include<algorithm>

#define pb push_back

#define mp make_pair

#define Maxn 1000010

#define Maxm 80002

#define LL __int64

#define Abs(x) ((x)>0?(x):(-x))

#define lson(x) (x<<1)

#define rson(x) (x<<1|1)

#define inf 100000

#define lowbit(x) (x&(-x))

#define Mod 1000000007

using namespace std;

int U[Maxn],D[Maxn],R[Maxn],L[Maxn],C[Maxn],S[Maxn],X[Maxn],H[1010],Q[1010],id;

void init(int m)

{

    int i;

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

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

        L[i+1]=i;

        R[i]=i+1;

        S[i]=0;

    }

    R[m]=0;

    id=m+1;

}

void ins(int r,int c)

{

    D[id]=D[c];

    U[id]=c;

    U[D[c]]=id;

    D[c]=id;

    S[c]++;

    if(H[r]<0)

        H[r]=L[id]=R[id]=id;

    else{

        L[id]=H[r];

        R[id]=R[H[r]];

        L[R[H[r]]]=id;

        R[H[r]]=id;

    }

    C[id]=c;

    X[id++]=r;

}

void Remove(int c)

{

    int i,j;

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

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

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

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

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

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

            S[C[j]]--;

        }

    }

}

void Resume(int c)

{

    int i,j;

    R[L[c]]=c;

    L[R[c]]=c;

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

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

            U[D[j]]=j;

            D[U[j]]=j;

            S[C[j]]++;

        }

    }

}

bool dfs(int k)

{

    int i,j,c,temp;

    if(R[0]==0){

        printf("%d",k);

        for(i=0;i<k;i++){

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

        }

        printf("\n");

        return true;

    }

    temp=inf;

    for(i=R[0];i;i=R[i]){

        if(S[i]<temp){

            temp=S[i];

            c=i;

        }

    }

    Remove(c);

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

        Q[k]=i;

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

            Remove(C[j]);

        if(dfs(k+1))

            return true;

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

            Resume(C[j]);

    }



    Resume(c);

    return false;

}

int main()

{

    int n,m,i,j,k,x;

    while(scanf("%d%d",&n,&m)!=EOF){

        init(m);

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

            scanf("%d",&k);

            H[i]=-1;

            while(k--){

                scanf("%d",&x);

                ins(i,x);

            }

        }

        if(!dfs(0))

            printf("NO\n");

    }

    return 0;

}

 

思路：裸的精确覆盖