日常练习16

Posted 2020-10-10

这道题就是典型的2-sat 不过这题因为严格相连所以应该是无向边QAQ

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using std::min;
const int M=2e3+7;
int read(){
    int ans=0,f=1,c=getchar();
    while(c<‘0‘||c>‘9‘){if(c==‘-‘) f=-1; c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){ans=ans*10+(c-‘0‘); c=getchar();}
    return ans*f;
}
int n,k,vis[2*M];
char ch[15];
int first[2*M],cnt,ans;
struct node{int from,to,next;}e[5*M];
void ins(int a,int b){e[++cnt]=(node){a,b,first[a]}; first[a]=cnt;}
void insert(int a,int b){ins(a,b); ins(b,a);}
int sum,ly;
int dfs(int x){
    if(vis[x^1]) return 0;
    vis[x]=1;
    sum++; if(x&1) ly++;
    for(int i=first[x];i;i=e[i].next){
        int now=e[i].to;
        if(vis[now]) continue;
        if (!dfs(now)) return 0;
    }
    return 1;
}
void two_sat(){
    memset(vis,0,sizeof(vis));
    for(int i=1;i<=n;i++){
        if(vis[i<<1]||vis[i<<1^1]) continue;
        sum=0; ly=0;
        if(dfs(i<<1)) ans=ans+std::max(ly,sum-ly);
        else return void(ans=-1);
    }
}
int main(){
    freopen("science.in","r",stdin);
    freopen("science.out","w",stdout);
    while(scanf("%d",&n)==1&&n){
        cnt=0; memset(first,0,sizeof(first));
        for(int i=1;i<=n;i++){
            scanf("%s",ch); k=read();
            scanf("%s",ch); scanf("%s",ch);
            if(ch[0]==‘t‘){
                if(k==i) continue;
                insert(i<<1,k<<1);
                insert(i<<1^1,k<<1^1);
            }
            else{
                insert(i<<1,k<<1^1);
                insert(i<<1^1,k<<1);
            }
        }
        ans=0; two_sat();
        if(ans>=0) printf("%d\\n",ans);
        else printf("Inconsistent\\n");
    }
    return 0;
}

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