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
 1 #include<cstdio>
 2 #include<cstring>
 3 const int MAXN = 2020; 
 4 const int MAXM = 1000010;
 5 struct Edge { int to, next; }edge[MAXM]; 
 6 int head[MAXN],tot,S[MAXN],top;//栈 ;
 7 void init(){tot = 0;memset(head, -1, sizeof(head));}
 8 void addedge(int u, int v) { edge[tot].to = v; edge[tot].next = head[u]; head[u] = tot++; }
 9 bool vis[MAXN];//染色标记，为true表示选择 
10 bool dfs(int u) {
11     if(vis[u^1])return false; 
12     if(vis[u])return true; 
13     vis[u] = true, S[top++] = u;
14     for(int i = head[u];i != -1;i = edge[i].next)    
15         if(!dfs(edge[i].to))return false;
16     return true; 
17 } 
18 bool Twosat(int n){  
19     memset(vis,false,sizeof(vis)); 
20     for(int i = 0;i < n;i += 2){
21         if(vis[i] || vis[i^1])continue;  
22         top = 0; 
23         if(!dfs(i)){  
24             while(top)vis[S[--top]] = false;    
25             if(!dfs(i^1)) return false;    
26         }   
27     }    
28     return true; 
29 } 
30 int main(){
31     int n,m,u,v,mm,ww;
32     while(~scanf("%d%d",&n,&m)){
33         init();      
34         while(m--){ 
35             scanf("%d%d%d%d",&u,&v,&mm,&ww);
36             u=u*2+mm,v=v*2+ww;
37             addedge(u,v^1);      
38             addedge(v,u^1);     
39         }      
40         if(Twosat(2*n))puts("YES");
41         else puts("NO"); 
42     }    
43     return 0; 
44 }
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