[2-SAT] [BZOJ1823] [JSOI2010]满汉全席

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[(http://www.lydsy.com/JudgeOnline/problem.php?id=1823)]

比较简单的2-SAT QwQ
0 1分别表示用汉式还是满式根据评委条件连边就行了

#include<cstdio>#include<cstring>#include<iostream>using namespace std;const int MaxN=205;const int MaxM=100005;int K,N,M,Cnt,EdgeCnt;int A[1005],B[1005];int Tot,Head[MaxN],Next[MaxM],To[MaxM];int Index,DFN[MaxN],Low[MaxN];int Top,Stack[MaxN],ID[MaxN];bool Vis[MaxN];struct Edge{    int u,v;}E[MaxM];void Add_Edge(int u,int v){    E[++EdgeCnt]=(Edge){u,v};    Next[++Tot]=Head[u];    To[Tot]=v;    Head[u]=Tot;}int Another(int x){    return (x%2?x+1:x-1);}void Init(){    int i,j,a,b;    char c1,c2;    scanf("%d%d",&N,&M);    for(i=1;i<=M;i++){        scanf("\n%c%d %c%d",&c1,&a,&c2,&b);        A[i]=a*2-(c1=='h');        B[i]=b*2-(c2=='h');    }    Tot=EdgeCnt=Cnt=0;    memset(Head,0,sizeof(Head));    for(i=1;i<=N*2;i++)        for(j=1;j<=M;j++){            if(A[j]==Another(i))                Add_Edge(i,B[j]);            if(B[j]==Another(i))                Add_Edge(i,A[j]);        }}void DFS(int u){    int i,v,tmp;    DFN[u]=Low[u]=++Index;    Vis[Stack[++Top]=u]=true;    for(i=Head[u];i;i=Next[i])        if(!DFN[v=To[i]]){            DFS(v);            Low[u]=min(Low[u],Low[v]);        }        else if(Vis[v])            Low[u]=min(Low[u],DFN[v]);    if(DFN[u]==Low[u]){        Cnt++;        do{            tmp=Stack[Top--];            ID[tmp]=Cnt;            Vis[tmp]=false;        }while(tmp!=u);    }}void Work(){    int i;    Index=Top=0;    memset(DFN,0,sizeof(DFN));    memset(Low,0,sizeof(Low));    for(i=1;i<=N*2;i++)        if(!DFN[i])            DFS(i);    for(i=1;i<=N*2;i+=2)        if(ID[i]==ID[i+1]){            puts("BAD");            return;        }    puts("GOOD");}int main(){    scanf("%d",&K);    while(K--){        Init();        Work();    }    return 0;}

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