【jzoj5305】【NOIP2017提高A组模拟8.18】【C】

description

solution

tarjan缩环，一个环贡献2^1，跑lca即可。

code

#include<set>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
#define LL long long
#define fo(i,j,k) for(int i=j;i<=k;i++)
#define fd(i,j,k) for(int i=j;i>=k;i--)
#define fr(i,j) for(int i=begin[j];i;i=next[i])
using namespace std;
int const mn=1e5+9,mm=3*1e5+9,mo=1e9+7;
int n,m,q,gra,u[mm],v[mm],begin[mn],to[mm],next[mm],tim,dfn[mn],low[mn],st[mn],ins[mn],
    lg2,f[mn],dep[mn],bel[mn],fa[mn][18],Pow[mn];
void insert(int u,int v){
    to[++gra]=v;
    next[gra]=begin[u];
    begin[u]=gra;
}
void dfs(int p,int q){
    dfn[p]=low[p]=++tim;
    ins[st[++st[0]]=p]=1;
    fr(i,p)if(i!=(q^1)){
        if(!dfn[to[i]]){
            dfs(to[i],i);
            low[p]=min(low[p],low[to[i]]);
        }else if(ins[to[i]])low[p]=min(low[p],dfn[to[i]]);
    }
    if(dfn[p]==low[p]){
        f[p]=st[st[0]]!=p;
        while(st[st[0]]!=p)bel[st[st[0]]]=p,ins[st[st[0]--]]=0;
        bel[st[st[0]]]=p,ins[st[st[0]--]]=0;
    }
}
void df2(int p,int q){
    dfn[p]=1;
    f[p]+=f[q];
    dep[p]=dep[q]+1;
    fa[p][0]=q;
    fr(i,p)if(to[i]!=q)df2(to[i],p);
}
int lc(int u,int v){
    if(dep[u]<dep[v])swap(u,v);
    int uu=u,vv=v;
    fd(i,lg2,0)if(dep[fa[u][i]]>=dep[v])u=fa[u][i];
    if(u==v)return Pow[f[uu]-f[fa[vv][0]]];
    fd(i,lg2,0)if(fa[u][i]!=fa[v][i])u=fa[u][i],v=fa[v][i];
    return Pow[f[uu]+f[vv]-f[fa[u][0]]-f[fa[u][1]]];
}
int main(){
    freopen("d.in","r",stdin);
    freopen("d.out","w",stdout);
    scanf("%d%d",&n,&m);
    gra=1;
    fo(i,1,m){
        scanf("%d%d",&u[i],&v[i]);
        insert(u[i],v[i]);
        insert(v[i],u[i]);
    }
    fo(i,1,n)if(!dfn[i])dfs(i,0);
    gra=1;
    fo(i,1,n)begin[i]=dfn[i]=0;
    fo(i,1,m)if(bel[u[i]]!=bel[v[i]]){
        insert(bel[u[i]],bel[v[i]]);
        insert(bel[v[i]],bel[u[i]]);
    }
    fo(i,1,n)if(!dfn[i])df2(i,0);
    lg2=log(n)/log(2);
    fo(j,1,lg2)fo(i,1,n)fa[i][j]=fa[fa[i][j-1]][j-1];
    scanf("%d",&q);
    Pow[0]=1;
    fo(i,1,n)Pow[i]=Pow[i-1]*2%mo;
    fo(cas,1,q){
        int u,v;
        scanf("%d%d",&u,&v);
        printf("%d\n",lc(bel[u],bel[v]));
    }
    return 0;
}