bzoj5049: 导航系统

#include<bits/stdc++.h>
const int N=1e5+7;
char ib[N*100],*ip=ib;
int _(){
    int x=0;
    while(*ip<48)++ip;
    while(*ip>47)x=x*10+*ip++-48;
    return x; 
}
int n,m,k,f[N];
std::vector<int>e[N];
int ed[N][2],tk=0;
int gf(int x){
    while(x!=x[f])x=x[f]=x[f][f];
    return x;
}
struct{
    int q[N],ql,qr;
    void clr(){ql=qr=0;}
    void push(int x,int d){
        ed[x][0]=tk;
        ed[x][1]=d;
        q[++qr]=x;
    }
    int pop(){return q[++ql];}
    int cnt(){return qr-ql;}
}qa,qb;
int que(){
    int a=_(),b=_();
    if(a==b)return 0;
    if(gf(a)!=gf(b))return -1;
    ++tk;
    qa.clr(),qb.clr();
    qa.push(a,1),qb.push(b,-1);
    for(;;){
        for(int t=qa.cnt();t;--t){
            int w=qa.pop(),d=ed[w][1]+1;
            for(unsigned i=0;i!=e[w].size();++i){
                int u=e[w][i];
                if(ed[u][0]==tk){
                    if(ed[u][1]<0)return d-ed[u][1]-2;
                }else qa.push(u,d);
            }
        }
        for(int t=qb.cnt();t;--t){
            int w=qb.pop(),d=ed[w][1]-1;
            for(unsigned i=0;i!=e[w].size();++i){
                int u=e[w][i];
                if(ed[u][0]==tk){
                    if(ed[u][1]>0)return ed[u][1]-d-2;
                }else qb.push(u,d);
            }
        }
    }
}
int main(){
    fread(ib,1,sizeof(ib),stdin);
    n=_(),m=_(),k=_();
    for(int i=1;i<=n;++i)f[i]=i,e[i].reserve(10);
    for(int i=0,a,b;i<m;++i){
        a=_(),b=_();
        e[a].push_back(b);
        e[b].push_back(a);
        f[gf(a)]=gf(b);
    }
    for(int i=1;i<=k;++i)printf("%d\n",que());
    return 0;
}