题目链接:http://acm.hust.edu.cn/vjudge/contest/view.action?cid=65998#problem/A
题意:求01矩阵的精确覆盖。
DLX学习资料:http://www.cnblogs.com/grenet/p/3145800.html
http://blog.csdn.net/mu399/article/details/7627862
#include <cstdio> #include <cstring> #include <string> #include <cmath> #include <iostream> #include <algorithm> #include <queue> #include <cstdlib> #include <stack> #include <vector> #include <set> #include <map> #define LL long long #define mod 10007 #define inf 0x3f3f3f3f #define N 100010 #define FILL(a,b) (memset(a,b,sizeof(a))) #define lson l,m,rt<<1 #define rson m+1,r,rt<<1|1 using namespace std; const int maxnode=100010; const int MaxN=1010; const int MaxM=1010; struct DLX { int n,m,size; int U[maxnode],D[maxnode],R[maxnode],L[maxnode],Row[maxnode],Col[maxnode]; int H[MaxN],S[MaxM]; int ansd,ans[MaxN]; void init(int _n,int _m) { 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) { ++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) { 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) { L[R[c]]=R[L[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]]; } bool Dance(int d) { 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; } }; DLX g; int main() { int n,m; while(scanf("%d%d",&n,&m)>0) { g.init(n,m); for(int i=1;i<=n;i++) { int num,j; scanf("%d",&num); while(num--) { scanf("%d",&j); g.Link(i,j); } } if(!g.Dance(0))puts("NO"); else { printf("%d",g.ansd); for(int i=0;i<g.ansd;i++)printf(" %d",g.ans[i]); puts(""); } } }