加深了对有向边意义的理解了。2-SAT
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 #include <algorithm> 5 #include <cmath> 6 using namespace std; 7 8 const int MAXN=2010; 9 const int MAXM=2100100; 10 11 int head[MAXN],dfn[MAXN],low[MAXN],st[MAXN],stop,belong[MAXN],tot,index,pat; 12 bool stack[MAXN]; 13 struct { 14 int u,v; 15 int next; 16 }edge[MAXM]; 17 int n,m; 18 int s1,s2; 19 20 void init(){ 21 stop=0; tot=0; index=0; pat=-1; 22 for(int i=0;i<2*n;i++){ 23 head[i]=-1; 24 dfn[i]=low[i]=0; 25 belong[i]=-1; 26 stack[i]=false; 27 } 28 } 29 30 void addedge(int u,int v){ 31 edge[tot].u=u; 32 edge[tot].v=v; 33 edge[tot].next=head[u]; 34 head[u]=tot++; 35 } 36 37 void tarjan(int u){ 38 int v; 39 dfn[u]=low[u]=++index; 40 st[stop++]=u; stack[u]=true; 41 for(int e=head[u];e!=-1;e=edge[e].next){ 42 v=edge[e].v; 43 if(dfn[v]==0){ 44 tarjan(v); 45 low[u]=min(low[u],low[v]); 46 } 47 else if(stack[v]){ 48 low[u]=min(low[u],dfn[v]); 49 } 50 } 51 if(dfn[u]==low[u]){ 52 pat++; 53 do{ 54 v=st[--stop]; 55 stack[v]=false; 56 belong[v]=pat; 57 }while(u!=v); 58 } 59 } 60 61 int main(){ 62 int u,v; 63 while(scanf("%d%d",&n,&m)!=EOF){ 64 init(); 65 for(int i=1;i<=m;i++){ 66 scanf("%d%d",&s1,&s2); 67 u=abs(s1)-1; 68 v=abs(s2)-1; 69 // cout<<u<<' '<<v<<endl; 70 if(s1>0&&s2>0){ 71 addedge(2*u,2*v+1); 72 addedge(2*v,2*u+1); 73 } 74 else if(s1>0&&s2<0){ 75 addedge(2*u,2*v); 76 addedge(2*v+1,2*u+1); 77 } 78 else if(s1<0&&s2>0){ 79 addedge(2*u+1,2*v+1); 80 addedge(2*v,2*u); 81 } 82 else{ 83 addedge(2*u+1,2*v); 84 addedge(2*v+1,2*u); 85 } 86 } 87 for(int i=0;i<2*n;i++){ 88 if(dfn[i]==0) 89 tarjan(i); 90 } 91 bool flag=true; 92 for(int i=0;i<n;i++){ 93 if(belong[i*2]==belong[i*2+1]){ 94 printf("0 "); 95 flag=false; 96 break; 97 } 98 } 99 if(flag) 100 printf("1 "); 101 } 102 }