poj 2723 Get Luffy Out 2-SAT

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
#include<iostream>
#define maxn 4505
using namespace std;
int low[maxn],dnf[maxn],que[maxn],tear,head[maxn],c[maxn],mark[maxn];
bool map[maxn][maxn];
vector<int>g[maxn];
void init(int n){
for(int i=1;i<=n;i++) g[i].clear();
}
int cal,tot;
void tarjin(int p){
dnf[p]=low[p]=cal++;
int i,k;
k=(int)g[p].size();
que[tear++]=p;
for(i=0;i<k;i++){
int v=g[p][i];
if(!dnf[v]){
tarjin(v);
low[p]=min(low[p],low[v]);//如果儿子就比较low
}
else if(!mark[v]){
low[p]=min(low[p],dnf[v]);//与栈里面的点进行比较，如果mark[i]有值就代表已经出栈了。
}
}
if(low[p]==dnf[p]){
while(tear>0){
mark[que[tear-1]]=tot;
if(que[tear-1]==p){
tear--;
break;
}
tear--;
}
tot++;
}
}
int solve(int n){
int i;
tear=0;
cal=1;
tot=1;
memset(dnf,0,sizeof(dnf));
memset(c,0,sizeof(c));
memset(mark,0,sizeof(mark));
for(i=1;i<=2*n;i++){
tear=0;
if(!dnf[i]) tarjin(i);
}
for(i=1;i<=n;i++){
if(mark[i]==mark[n+i]) return 0;
}
return 1;
}
void add(int a,int b){
g[a].push_back(b);
}
struct pi{
int a;
int b;
}pp[maxn],pp1[maxn];
int main()
{
int i,n,m;
while(cin>>n>>m){
if(n==0&&m==0) break;
init(4*n);
for(i=1;i<=n;i++){
scanf("%d%d",&pp[i].a,&pp[i].b);
pp[i].a++;
pp[i].b++;
}
for(i=1;i<=m;i++){
scanf("%d%d",&pp1[i].a,&pp1[i].b);
pp1[i].a++;
pp1[i].b++;
}
int le,ri,mid;
le=1;
ri=m;
while(le<=ri){
mid=(le+ri)/2;
init(4*n);
for(i=1;i<=n;i++){
add(pp[i].a,2*n+pp[i].b);
add(pp[i].b,2*n+pp[i].a);
}
for(i=1;i<=mid;i++){
add(2*n+pp1[i].a,pp1[i].b);
add(2*n+pp1[i].b,pp1[i].a);
}
if(solve(2*n)) le=mid+1;
else ri=mid-1;
}
printf("%d\n",ri);
}
}