n个国家 每个国家有两个代表 桥求选出 n个人成立世界和平委员会 有m条关系 a与b 关系差不能同时选中 求选中人的最小字典序
2-sat的入门题
调试了半天发现那个博客就是错的心态崩了
#include#include #include #include using namespace std;//input by bxd#define rep(i,a,b) for(int i=(a);i<=(b);i++)#define repp(i,a,b) for(int i=(a);i>=(b);--i)#define RI(n) scanf("%d",&(n))#define RII(n,m) scanf("%d%d",&n,&m)#define RIII(n,m,k) scanf("%d%d%d",&n,&m,&k)#define RS(s) scanf("%s",s);#define ll long long#define pb push_back#define REP(i,N) for(int i=0;i<(N);i++)#define CLR(A,v) memset(A,v,sizeof A)//#define inf 0x3f3f3f3fconst int N=16000;const int M=5*N; int n,m;int pos,head[N],pos2,head2[N];struct Edge{ int to,nex;}edge[M],edge2[M];void add(int a,int b){ edge[++pos].nex=head[a]; head[a]=pos; edge[pos].to=b;}void add2(int a,int b){ edge2[++pos2].nex=head2[a]; head2[a]=pos2; edge2[pos2].to=b;}int tot,ind,cnt,Stack[N],dfn[N],low[N],belong[N],in[N],vis[N];int f[N];void tarjan(int x){ dfn[x]=low[x]=++tot; Stack[++ind]=x; vis[x]=1; for(int i=head[x];i;i=edge[i].nex) { int v=edge[i].to; if(!dfn[v]) { tarjan(v); low[x]=min(low[x],low[v]); } else if(vis[v]) low[x]=min(low[x],low[v]); } if(dfn[x]==low[x]) { cnt++;int v; do { v=Stack[ind--]; vis[v]=0; belong[v]=cnt; } while(v!=x); }}int ans[N];void init(){ cnt=pos=ind=tot=pos2=0; CLR(head2,0); CLR(head,0); CLR(vis,0); CLR(in,0); CLR(Stack,0); CLR(dfn,0); CLR(low,0); CLR(ans,0);}void builddag(){ rep(i,0,2*n-1) { int u=belong[i]; for(int j=head[i];j;j=edge[j].nex) { int v=belong[edge[j].to]; if(v!=u) add2(v,u),in[u]++; } }}void solve(){ for(int i=0;i<2*n;i+=2) if(belong[i]==belong[i^1]) { printf("NIE\n"); return ; } else f[ belong[i] ]=belong[i+1],f[belong[i+1]]=belong[i]; builddag(); queue q; rep(i,1,cnt) if(!in[i]) q.push(i); while(!q.empty()) { int u=q.front();q.pop(); if(!ans[u]) ans[u]=1,ans[f[u]]=2; for(int i=head2[u];i;i=edge2[i].nex) { int v=edge2[i].to; if(--in[v]==0)q.push(v); } } for(int i=0;i<2*n;i+=2) if(ans[belong[i]]==1) printf("%d\n",i+1); else printf("%d\n",i+2);}int main(){ while(RII(n,m)==2) { init(); rep(i,1,m) { int a,b;RII(a,b); b--;a--;add(a,b^1);add(b,a^1); } rep(i,0,2*n-1) if(!dfn[i]) tarjan(i); solve(); } return 0;}
贴上2-sat模板：
#include#include #include #include using namespace std;//input by bxd#define rep(i,a,b) for(int i=(a);i<=(b);i++)#define repp(i,a,b) for(int i=(a);i>=(b);--i)#define RI(n) scanf("%d",&(n))#define RII(n,m) scanf("%d%d",&n,&m)#define RIII(n,m,k) scanf("%d%d%d",&n,&m,&k)#define RS(s) scanf("%s",s);#define ll long long#define pb push_back#define REP(i,N) for(int i=0;i<(N);i++)#define CLR(A,v) memset(A,v,sizeof A)//#define inf 0x3f3f3f3fconst int N=8005*2;const int M=90000;int n,m;int head[M<<1],pos;struct Edge{ int to,nex;}edge[M<<1];void add(int a,int b){ edge[++pos].nex=head[a]; head[a]=pos; edge[pos].to=b;}void init(){ pos=0; CLR(head,0);}int cnt,vis[N],s[N];bool dfs(int x){ if(vis[x^1])return 0; if(vis[x])return 1; s[cnt++]=x; vis[x]=1; for(int i=head[x];i;i=edge[i].nex) if(!dfs(edge[i].to)) return 0; return 1;}bool twosat(){ CLR(vis,0); for(int i=0;i<2*n;i+=2) if(!vis[i]&&!vis[i+1]){ cnt=0; if(!dfs(i)){ while(cnt)vis[ s[--cnt] ]=0; if(!dfs(i^1))return 0; } } return 1;}int main(){ int a,b; while(RII(n,m)!=EOF) { init(); rep(i,1,m) { RII(a,b); a--;b--; add(a,b^1); add(b,a^1); } if(twosat()) { for(int i=0;i<2*n;i+=2) { if(vis[i])printf("%d\n",i+1); else printf("%d\n",i+2); } } else printf("NIE\n"); } return 0;}