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POJ-3207-Ikki's Story IV - Panda's Trick(2-sat模板)

2-sat模板提。

代码:

#include<iostream>
#include<cstdio>
#include<cmath>
#include<map>
#include<queue>
#include<vector>
#include<cstring>
#include<algorithm>
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rev(i,a,b) for(int i=(a);i>=(b);i--)
#define clr(a,x) memset(a,x,sizeof a)
#define INF 0x3f3f3f3f
typedef long long LL;
using namespace std;

const int maxn=1005;
const int maxm=2000005;

int first[maxn],ecnt,u[maxm],v[maxm],nex[maxm];
int low[maxn],dfn[maxn],stck[maxn],belong[maxn];
int indx,top,scc;
bool ins[maxn];
int num[maxn];
int n,m;
int a[maxn],b[maxn];

void tarjan(int u)
{
    low[u]=dfn[u]=++indx;
    stck[top++]=u;
    ins[u]=1;
    for(int e=first[u];~e;e=nex[e])
    {
        if(!dfn[v[e]])
        {
            tarjan(v[e]);
            low[u]=min(low[u],low[v[e]]);
        }
        else if(ins[v[e]])low[u]=min(low[u],dfn[v[e]]);
    }
    if(low[u]==dfn[u])
    {
        int v;
        scc++;
        do
        {
            v=stck[--top];
            ins[v]=false;
            belong[v]=scc;
            num[scc]++;
        }while(v!=u);
    }
}
void solve(int n)
{
    clr(dfn,0);
    clr(ins,0);
    clr(num,0);
    indx=scc=top=0;
    for(int i=1;i<=n;i++)
        if(!dfn[i])tarjan(i);
}
void add_(int a,int b)
{
    u[ecnt]=a;
    v[ecnt]=b;
    nex[ecnt]=first[a];
    first[a]=ecnt++;
}
void init()
{
    ecnt=0;
    clr(first,-1);
}
inline bool pan(int a,int b,int c,int d)
{
    return (a<b&&b<c&&c<d)||(d<c&&c<b&&b<a);
}
int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        for(int i=1;i<=m;i++)
        {
            scanf("%d%d",&a[i],&b[i]);
            if(a[i]>b[i])swap(a[i],b[i]);
        }
        init();
        for(int i=1;i<=m;i++)
            for(int j=1;j<=m;j++)
            if(pan(a[i],a[j],b[i],b[j])){
                add_(i,j+m);
                add_(j,i+m);
                add_(i+m,j);
                add_(j+m,i);
            }
        solve(2*m);
        int ans=1;
        for(int i=1;i<=m&&ans;i++)
            if(belong[i]==belong[i+m])ans=0;
        if(ans)puts("panda is telling the truth...");
        else puts("the evil panda is lying again");
    }
    return 0;
}


POJ-3207-Ikki's Story IV - Panda's Trick(2-sat模板)