POJ 3678

  1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <string.h>
  5 #include <algorithm>
  6 #include <cmath>
  7 
  8 using namespace std;
  9 
 10 const int MAXN=2050;
 11 const int MAXM=4001000;
 12 int n,m;
 13 char s[10];
 14 int head[MAXN],dfn[MAXN],low[MAXN],st[MAXN],tot,stop,indx,pat,belong[MAXN];
 15 bool stack[MAXN];
 16 
 17 struct{
 18     int u,v;
 19     int next;
 20 }edge[MAXM];
 21 
 22 void addedge(int u,int v){
 23     edge[tot].u=u;
 24     edge[tot].v=v;
 25     edge[tot].next=head[u];
 26     head[u]=tot++;
 27 }
 28 
 29 void tarjan(int u){
 30     int v;
 31     dfn[u]=low[u]=++indx;
 32     st[stop++]=u;
 33     stack[u]=true;
 34     for(int e=head[u];e!=-1;e=edge[e].next){
 35         v=edge[e].v;
 36         if(dfn[v]==0){
 37             tarjan(v);
 38             low[u]=min(low[u],low[v]);
 39         }
 40         else if(stack[v]){
 41             low[u]=min(low[u],dfn[v]);
 42         }
 43     }
 44     if(dfn[u]==low[u]){
 45         pat++;
 46         do{
 47             v=st[--stop];
 48             belong[v]=pat;
 49             stack[v]=false;
 50         }while(u!=v);
 51     }
 52 }
 53 
 54 int main(){
 55     int u,v,c;
 56     while(scanf("%d%d",&n,&m)!=EOF){
 57         
 58         memset(head,-1,sizeof(head));
 59         tot=stop=indx=pat=0;
 60         memset(dfn,0,sizeof(dfn));
 61         memset(low,0,sizeof(low));
 62         memset(stack,false,sizeof(stack));
 63         memset(belong,0,sizeof(belong));
 64         
 65         for(int i=0;i<m;i++){
 66             scanf("%d%d%d%s",&u,&v,&c,s);
 67             if(strcmp(s,"OR")==0){
 68                 if(c==0){
 69                     addedge(2*u,2*u+1);
 70                     addedge(2*v,2*v+1);
 71                 }
 72                 else{
 73                     addedge(2*u+1,2*v);
 74                     addedge(2*v+1,2*u);
 75                 }
 76             }
 77             else if(strcmp(s,"AND")==0){
 78                 if(c==0){
 79                     addedge(2*u,2*v+1);
 80                     addedge(2*v,2*u+1);
 81                 }
 82                 else {
 83                     addedge(2*u+1,2*u);
 84                     addedge(2*v+1,2*v);
 85                 }
 86             }
 87             else{
 88                 if(c==0){
 89                     addedge(2*u,2*v);
 90                     addedge(2*v,2*u);
 91                     addedge(2*u+1,2*v+1);
 92                     addedge(2*v+1,2*u+1);
 93                 }
 94                 else{
 95                     addedge(2*u,2*v+1);
 96                     addedge(2*u+1,2*v);
 97                     addedge(2*v,2*u+1);
 98                     addedge(2*v+1,2*u);
 99                 }
100             }
101         }
102         for(int i=0;i<2*n;i++){
103             if(dfn[i]==0){
104                 tarjan(i);
105             }
106         }
107         
108         bool flag=true;
109         for(int i=0;i<n;i++){
110             if(belong[i*2]==belong[2*i+1]){
111                 printf("NO\n");
112                 flag=false;
113                 break;
114             }
115         }
116         if(flag)
117         printf("YES\n");
118     }
119     return 0;
120 }