poj 3207（2-SAT）

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<stack>
using namespace std;
const int MAXN=1004;
int n,m;
int head[MAXN],edge=0,low[MAXN],dfn[MAXN],bel[MAXN],tim=0,snt=0;
struct EDGE {
int v,nxt;
}e[MAXN*MAXN];
bool ins[MAXN],f=true;
int x[MAXN>>1],y[MAXN>>1];
stack<int> S;
inline int read() {
int x=0;char c=getchar();
while (c<'0'||c>'9') c=getchar();
while (c>='0'&&c<='9') x=x*10+c-'0',c=getchar();
return x;
}
inline void adde(int u,int v) {
e[edge].nxt=head[u],e[edge].v=v,head[u]=edge++;
}
void dfs(int p) {
dfn[p]=low[p]=++tim;
S.push(p),ins[p]=true;
for (int i=head[p];~i;i=e[i].nxt) {
int v=e[i].v;
if (!dfn[v]) {
dfs(v);
low[p]=min(low[p],low[v]);
}
else if (ins[v]) low[p]=min(low[p],dfn[v]);
}
if (dfn[p]==low[p]) {
++snt;
while (true) {
int t=S.top();
S.pop();
bel[t]=snt;
ins[t]=false;
if (t==p) break;
}
}
}
int main() {
memset(head,-1,sizeof(head));
memset(dfn,0,sizeof(dfn));
memset(ins,false,sizeof(ins));
n=read(),m=read();
for (int i=1;i<=m;++i) {
x[i]=read(),y[i]=read();
if (x[i]>y[i]) x[i]^=y[i]^=x[i]^=y[i];
}
for (int i=1;i<m;++i)
for (int j=i+1;j<=m;++j)
if (x[i]>x[j]&&x[i]<y[j]&&y[i]>y[j]||x[j]>x[i]&&x[j]<y[i]&&y[j]>y[i]) {
adde(i,j+m);
adde(j+m,i);
adde(i+m,j);
adde(j,i+m);
}
for (int i=1;i<=(m<<1);++i)
if (!dfn[i]) dfs(i);
for (int i=1;i<=m;++i)
if (bel[i]==bel[i+m]) f=false;
puts(f?"panda is telling the truth...":"the evil panda is lying again");
return 0;
}