POJ 3683 Priest John's Busiest Day

2-SAT经典问题

#include<cstdio> #include<string.h> #include<math.h> #include<stack> #define N 2010 #define M N*N*3 using namespace std; struct edge{ int v,next; }edge[M]; int n; int s[N],t[N],seq[N]; int cnt,head1[N],head2[N],head3[N]; int scc,index,dfn[N],low[N],belong[N]; int top,sstack[N]; bool instack[N],vis[N]; int d[N],col[N]; void addedge(int u,int v,int *head) { edge[cnt].v=v; edge[cnt].next=head[u]; head[u]=cnt++; } int MAX(int a,int b){ return a>b?a:b; } int MIN(int a,int b){ return a>b?b:a; } void tarjan(int u) { dfn[u]=low[u]=++index; sstack[++top]=u; instack[u]=true; for(int j=head1[u];j!=-1;j=edge[j].next) { int v=edge[j].v; if(dfn[v]==0) { tarjan(v); low[u]=MIN(low[v],low[u]); } else if(instack[v]) { low[u]=MIN(low[u],dfn[v]); } } if(dfn[u]==low[u]) { scc++; while(1) { int tmp=sstack[top--]; addedge(scc,tmp,head3); instack[tmp]=false; belong[tmp]=scc; if(tmp==u) break; } } } void make_graph(){ int i,j; for(i=1;i<=2*n;i++){ for(j=head1[i];j!=-1;j=edge[j].next){ int v=edge[j].v; if(belong[i]!=belong[v]){ addedge(belong[v],belong[i],head2); } } } } bool ok(int i,int j){ if(s[i]>=t[j] || t[i]<=s[j]) return false; return true; } bool check(){ int i; for(i=1;i<=n;i++){ if(belong[i*2]==belong[i*2-1]) return false; } return true; } void topo(){ int i,j; top=0; stack<int>sta; for(i=1;i<=scc;i++) for(j=head2[i];j!=-1;j=edge[j].next) d[edge[j].v]++; for(i=1;i<=scc;i++){ if(!d[i]) sta.push(i); } while(!sta.empty()){ int u=sta.top(); sta.pop(); seq[++top]=u; for(i=head2[u];i!=-1;i=edge[i].next){ int v=edge[i].v; d[v]--; if(!d[v]) sta.push(v); } } } void colour(){ int i,j,k; for(j=1;j<=top;j++){ int u=seq[j]; if(col[u]==0){ col[u]=1; for(i=head3[u];i!=-1;i=edge[i].next){ int v=edge[i].v; col[belong[((v-1)^1)+1]]=-1; for(k=head2[belong[((v-1)^1)+1]];k!=-1;k=edge[k].next) //异或的优先性低 col[edge[k].v]=-1; } } } } void printf_path(){ int i,j; for(i=1;i<=n;i++){ if(col[belong[i*2]]==1){ printf("%02d:%02d %02d:%02d\n",s[i*2]/60,s[i*2]%60,t[i*2]/60,t[i*2]%60); } else{ printf("%02d:%02d %02d:%02d\n",s[i*2-1]/60,s[i*2-1]%60,t[i*2-1]/60,t[i*2-1]%60); } } } int main(){ int i,j; scanf("%d",&n); memset(head1,-1,sizeof(head1));cnt=0; memset(head2,-1,sizeof(head2)); memset(head3,-1,sizeof(head3)); for(i=1;i<=n;i++){ int u,v,tem; scanf("%d:%d",&u,&v); s[2*i-1]=u*60+v; scanf("%d:%d",&u,&v); t[2*i]=u*60+v; scanf("%d",&tem); t[2*i-1]=s[2*i-1]+tem; s[2*i]=t[2*i]-tem; } for(i=1;i<=n;i++){ for(j=i+1;j<=n;j++){ if(ok(2*i,2*j)){ addedge(2*i,2*j-1,head1); addedge(2*j,2*i-1,head1); } if(ok(2*i-1,2*j)){ addedge(2*i-1,2*j-1,head1); addedge(2*j,2*i,head1); } if(ok(2*i,2*j-1)){ addedge(2*i,2*j,head1); addedge(2*j-1,2*i-1,head1); } if(ok(2*i-1,2*j-1)){ addedge(2*i-1,2*j,head1); addedge(2*j-1,2*i,head1); } } } scc=0; for(i=1;i<=2*n;i++) if(!dfn[i]) tarjan(i); if(!check()){ printf("NO\n"); } else{ printf("YES\n"); make_graph(); topo(); colour(); printf_path(); } }