主要利用了宏和stderr...

#define enable_debug

#ifdef enable_debug

FILL some macros/functions here

#else

/// set some debug functions to NULL

#endif

1. 输出到stderr

#define debug(...) { \

   fprintf(stderr,__VA_ARGS__); \

   fflush(stderr); \

} \

2. 若debug则插入一段代码

#define ProgDBG(...) { __VA_ARGS__; }

example.

#include "cstdio"

#include "vector"

#include "cstring"

#include "cstdlib"

#include "algorithm"

#define pb push_back

#define frp(x,y,z) freopen(#x"."#z,#y,std##z);

using namespace std;

const int

	maxn =  50010,

	maxm = 100010;

struct node;

struct ed{

	node*f,*t;

	ed*r;

} AlEd[maxn<<2],*p=AlEd;

struct node{

	vector<ed*> To,Eto;

	int id,nid,color;

	int dist1,dist2;

} nd [maxn];

inline void ade(int f,int t){

	*p=(ed){nd+f,nd+t,p+1};

	nd[f].Eto.pb(p);

	nd[f].To.pb(p++);

	*p=(ed){nd+t,nd+f,p-1};

	nd[t].Eto.pb(p);

	nd[t].To.pb(p++);

}

struct qry{ int f,t,id; } qrs[maxm];

int nowColor,ans[maxm];

//#define idbg

#ifdef idbg

	#define debug(...) {fprintf(stderr,__VA_ARGS__);fflush(stderr);}

	// #define assert(...)

	inline void tensenx(int&p,int b){

		if(b<p) p=b;

	}

	#define xassert(x,...) if(!(x)){ \

		debug(__VA_ARGS__);exit(3); \

	}

	#define tensen(a,...) { \

		int t=__VA_ARGS__; \

		xassert(t >= 0,"Tensened with: %d, code:\n" #__VA_ARGS__,t); \

		tensenx(a,t); \

	}

	#define ProgDBG(...) { __VA_ARGS__; }

#else

	#define debug(...)

	inline void tensen(int&p,int b){

		if(b<p) p=b;

	}

	#define ProgDBG(...)

#endif

typedef vector<node*> vn;

typedef vector<qry*>  vq;

/// generate bfs functions

#define bfsx(x) inline void bfs##x(node*from){ \

	ProgDBG( debug("BFS"#x"\n"); ) \

	static node*queue[maxn]; \

	int ql=0,qr=1,col=from->color; \

	queue[0]=from; \

	from->dist##x=0; \

	while(ql-qr){ \

		node*v=queue[ql++]; \

		ProgDBG( \

			debug("Vis %d\n",v->id); \

		) \

		for(int i=0,_=v->Eto.size();i<_;++i){ ed*p=v->Eto[i]; \

			if(p->t->color==col && !(~p->t->dist##x)){ \

				p->t->dist##x=v->dist##x+1; \

				queue[qr++]=p->t; \

			}else{ \

				ProgDBG( \

					if(p->t->color!=col){ \

						debug("%d color not match\n",p->t->id); \

					}else{ \

						debug("%d dist"#x"(%d) mismatch\n",p->t->id,p->t->dist##x); \

					} \

				) \

			} \

		} \

	} \

}

/// bfs1 & bfs2

bfsx(1);

bfsx(2);

void div(vn nodeList,vq qryList){

	ProgDBG(

		debug("Div Nodes: ");

		for(int i=0,_=nodeList.size();i<_;++i){

			debug("%d ",nodeList[i]->id);

		}

		debug("\n");

	);

	if(nodeList.size()<=3){

		for(int i=0,_=qryList.size();i<_;++i){

			tensen(ans[qryList[i]->id],qryList[i]->f!=qryList[i]->t);

		}

	}else{

		int color=nowColor++;

		for(int i=0,_=nodeList.size();i<_;++i){

			nodeList[i]->color=color;

			nodeList[i]->nid  =i;

			nodeList[i]->dist1=-1;

			nodeList[i]->dist2=-1;

		}

		/// Find edge to cut.

		int len=nodeList.size();

		int maxlen=len;

		ed*cur=NULL;

		for(int i=0,_=nodeList.size();i<_;++i){

			for(int j=0,_=nodeList[i]->Eto.size();j<_;++j){ ed*p=nodeList[i]->Eto[j];

				if(p->t->color==color){

					ProgDBG(

						debug("Has Edge: %d -> %d\n",p->f->id,p->t->id);

					)

					int fx=p->f->nid,

					    tx=p->t->nid;

					if(fx>tx) std::swap(fx,tx);

					int na=fx+len-tx+1;

					int nb=tx-fx+1;

					na=na>nb?na:nb;

					if(na<maxlen) maxlen=na, cur=p;

				}

			}

		}

		/// Calculate answer through this edge and divide the queries

		bfs1(cur->f);

		bfs2(cur->t);

		int ef=cur->f->nid;

		int et=cur->t->nid;

		ProgDBG(

			debug("Cut edge: (NID) %d %d\n",ef,et);

			debug("           (ID) %d %d\n",cur->f->id,cur->t->id);

		)

		if(ef>et) std::swap(ef,et);

		vq qryA,qryB;

		for(int i=0,_=qryList.size();i<_;++i){

			qry*p=qryList[i];

			tensen(ans[p->id],nd[p->f].dist1+nd[p->t].dist1);

			tensen(ans[p->id],nd[p->f].dist1+nd[p->t].dist2+1);

			tensen(ans[p->id],nd[p->f].dist2+nd[p->t].dist1+1);

			debug("%d %d %d %d\n",p->f,nd[p->f].dist2,p->t,nd[p->t].dist2);

			tensen(ans[p->id],nd[p->f].dist2+nd[p->t].dist2);

			int qf=nd[p->f].nid;

			int qt=nd[p->t].nid;

			if(qf>qt) std::swap(qf,qt);

			if(qf==ef && qt==et) continue;

			if(qf<=ef){

				if(qt>=et || qt<=ef) qryA.pb(p);

			}else

			if(qf>=et) qryA.pb(p);

			if(qf>=ef && qf<=et){

				if(qt>=ef && qt<=et) qryB.pb(p);

			}

		}

		/// divide nodes

		vn ndA,ndB;

		for(int i=0,_=nodeList.size();i<_;++i){

			if(i<=ef) ndA.pb(nodeList[i]);

			if(i>=et) ndA.pb(nodeList[i]);

			if(i>=ef && i<=et) ndB.pb(nodeList[i]);

		}

		vector<ed*> pat=nodeList[ef]->Eto;

		vector<ed*> pbt=nodeList[et]->Eto;

		vector<ed*> qat, qbt, xat, xbt;

		for(int i=0,_=pat.size();i<_;++i){

			if(pat[i]->t->nid<=ef) qat.pb(pat[i]);

			if(pat[i]->t->nid>=et) qat.pb(pat[i]);

			if(pat[i]->t->nid>=ef && pat[i]->t->nid<=et) qbt.pb(pat[i]);

		}

		for(int i=0,_=pbt.size();i<_;++i){

			if(pbt[i]->t->nid<=ef) xat.pb(pbt[i]);

			if(pbt[i]->t->nid>=et) xat.pb(pbt[i]);

			if(pbt[i]->t->nid>=ef && pbt[i]->t->nid<=et) xbt.pb(pbt[i]);

		}

		nodeList[ef]->Eto=qat; nodeList[et]->Eto=xat;

		div(ndA,qryA);

		nodeList[ef]->Eto=qbt; nodeList[et]->Eto=xbt;

		div(ndB,qryB);

	}

}

int main(){

	frp(B,r,in);

	frp(B,w,out);

	int n; scanf("%d",&n);

	for(int i=1;i<=n;++i) ade(i,i%n+1),nd[i].id=i;

	for(int i=3;i< n;++i){

		int a,b; scanf("%d%d",&a,&b); ade(a,b);

	}

	int q; scanf("%d",&q);

	for(int i=1;i<=q;++i){ scanf("%d%d",&qrs[i].f,&qrs[i].t); qrs[i].id=i; }

	vn A; vq B;

	for(int i=1;i<=n;++i) A.pb(nd+i);

	for(int i=1;i<=q;++i) B.pb(qrs+i);

	memset(ans,0x3f,sizeof(ans));

	div(A,B);

	for(int i=1;i<=q;++i) printf("%d\n",ans[i]);

	return 0;

}