LUOGU P4171 [JSOI2010]满汉全席

传送门

解题思路

2-SAT 裸题。

代码

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<cstdlib>
#include<algorithm>

using namespace std;
const int MAXN = 1005;

inline int rd(){
    int x=0,f=1;char ch=getchar();
    while(!isdigit(ch)) {f=ch=='-'?-1:1;ch=getchar();}
    while(isdigit(ch))  {x=(x<<1)+(x<<3)+ch-'0';ch=getchar();}
    return x*f;
}

int n,m,T,head[MAXN],cnt,col_num,num;
int to[MAXN<<1],nxt[MAXN<<1],bl[MAXN];
int stk[MAXN],top,low[MAXN],dfn[MAXN];
bool vis[MAXN];

inline void add(int bg,int ed){
    to[++cnt]=ed,nxt[cnt]=head[bg],head[bg]=cnt;
}

void tarjan(int x){
    low[x]=dfn[x]=++num;vis[x]=1;stk[++top]=x;
    for(register int i=head[x];i;i=nxt[i]){
        int u=to[i];
        if(!dfn[u]) {
            tarjan(u);
            low[x]=min(low[x],low[u]);
        }
        else if(vis[u]) low[x]=min(low[x],dfn[u]);
    }
    if(low[x]==dfn[x]){
        vis[x]=0;bl[x]=++col_num;
        while(stk[top]!=x){
            vis[stk[top]]=0;
            bl[stk[top--]]=col_num;
        }top--;
    }
}

int main(){
    T=rd();char c1[10],c2[10];
    while(T--){
        memset(head,0,sizeof(head));
        memset(bl,0,sizeof(bl));
        memset(dfn,0,sizeof(dfn));
        memset(low,0,sizeof(low));
        memset(nxt,0,sizeof(nxt));
        memset(to,0,sizeof(to));
        top=num=col_num=cnt=0;
        n=rd();m=rd();bool flag=false;
        for(register int i=1;i<=m;i++){
            scanf("%s%s",c1+1,c2+1);
            int sx=0,sy=0,tx=0,ty=0,x=0,y=0,t1=2,t2=2;
            if(c1[1]=='m') sx=1;if(c2[1]=='m') sy=1;
            tx=sx^1,ty=sy^1;
            while(isdigit(c1[t1])) x=(x<<1)+(x<<3)+c1[t1++]-'0';
            while(isdigit(c2[t2])) y=(y<<1)+(y<<3)+c2[t2++]-'0';
//          cout<<x<<" "<<y<<endl;
            add(x<<1|tx,y<<1|sy);add(y<<1|ty,x<<1|sx);  
        }   
        for(register int i=2;i<=(n<<1|1);i++) if(!dfn[i]) tarjan(i);
        for(register int i=1;i<=n;i++)
            if(bl[i<<1]==bl[i<<1|1]) {
                puts("BAD");flag=1;
                break;
            }
        if(!flag) puts("GOOD");
    }
    return 0;
}