poj 2723 Get Luffy Out

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <ctype.h>
#include <math.h>
#include <time.h>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <vector>
#include <string>
#include <iostream>
#include <algorithm>
using namespace std;

#define ull unsigned __int64
//#define ll __int64
//#define ull unsigned long long
#define ll long long
#define son1 New(p.xl,xm,p.yl,ym),(rt<<2)-2
#define son2 New(p.xl,xm,min(ym+1,p.yr),p.yr),(rt<<2)-1
#define son3 New(min(xm+1,p.xr),p.xr,p.yl,ym),rt<<2
#define son4 New(min(xm+1,p.xr),p.xr,min(ym+1,p.yr),p.yr),rt<<2|1
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define middle (l+r)>>1
#define MOD 1000000007
#define esp (1e-8)
const int INF=0x3F3F3F3F;
const double DINF=10000.00;
//const double pi=acos(-1.0);
const int M=5010;
int min(int x,int y){return x<y? x:y;}
int max(int x,int y){return x>y? x:y;}
void swap(int& x,int& y){int t=x;x=y;y=t;}
int T,cas;

vector<int>init[M];
int low[M],pre[M],idx[M],ss[M],Hash[M];
int n,nn,Index,top,m,N;

void dfs(int u){
low[u]=pre[u]=++Index;
ss[++top]=u;
for(int i=0;i<init[u].size();i++){
int v=init[u][i];
if(pre[v]==-1) dfs(v),low[u]=min(low[u],low[v]);
else if(idx[v]==-1) low[u]=min(low[u],pre[v]);
}
if(low[u]==pre[u]){
int v=-1;
++nn;
while(u!=v) idx[v=ss[top--]]=nn;
}
}

void Tarjan(){
memset(idx,-1,sizeof(int)*(n+1));
memset(pre,-1,sizeof(int)*(n+1));
Index=top=nn=0,ss[0]=-1;
for(int u=1;u<=n;u++) if(pre[u]==-1) dfs(u);
}

bool _sof(){
Tarjan();
for(int i=1;i<=n;i+=2) if(idx[i]==idx[i+1]) return false;
return true;
}

void _init(){
int u,uu,v,vv,i;
for(i=1,n=N<<2;i<=n;i++) init[i].clear();
for(i=0;i<N;i++){
scanf("%d%d",&u,&v);
u=u<<1|1,uu=u+1;
v=v<<1|1,vv=v+1;
init[u].push_back(vv);
init[v].push_back(uu);
}
int ret=0;
for(i=1;i<=m;i++){
scanf("%d%d",&u,&v);
u=u<<1|1,uu=u+1;
v=v<<1|1,vv=v+1;
init[uu].push_back(v);
init[vv].push_back(u);
if(_sof())  ret=i;
}
printf("%d\n",ret);
}

int main(){
//freopen("1.in","r",stdin);
//freopen("1.out","w",stdout);
//_init()
//scanf("%d",&T);for(cas=1;cas<=T;cas++) _init();
while(scanf("%d%d",&N,&m) && (N||m))  _init();
return 0;
}