hdu_3062_Party(2-SAT)

题目连接：http://acm.hdu.edu.cn/showproblem.php?pid=3062/

题意：2-SAT的裸题

题解：直接上模版

 #include<cstdio>
 #include<cstring>
 const int MAXN = ;
 const int MAXM = ;
 struct Edge { int to, next; }edge[MAXM];
 int head[MAXN],tot,S[MAXN],top;//栈 ;
 void init(){tot = ;memset(head, -, sizeof(head));}
 void addedge(int u, int v) { edge[tot].to = v; edge[tot].next = head[u]; head[u] = tot++; }
 bool vis[MAXN];//染色标记，为true表示选择
 bool dfs(int u) {
     if(vis[u^])return false;
     if(vis[u])return true;
     vis[u] = true, S[top++] = u;
     for(int i = head[u];i != -;i = edge[i].next)
         if(!dfs(edge[i].to))return false;
     return true;
 }
 bool Twosat(int n){
     memset(vis,false,sizeof(vis));
     for(int i = ;i < n;i += ){
         if(vis[i] || vis[i^])continue;
         top = ;
         if(!dfs(i)){
             while(top)vis[S[--top]] = false;
             if(!dfs(i^)) return false;
         }
     }
     return true;
 }
 int main(){
     int n,m,u,v,mm,ww;
     while(~scanf("%d%d",&n,&m)){
         init();
         while(m--){
             scanf("%d%d%d%d",&u,&v,&mm,&ww);
             u=u*+mm,v=v*+ww;
             addedge(u,v^);
             addedge(v,u^);
         }
         if(Twosat(*n))puts("YES");
         else puts("NO");
     }
     return ;
 }