[Luogu4320]

必经点数==圆方树上两点路径上圆点数

也就等于边数/2+1

没什么好说的 , 看代码

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#define debug(...) fprintf(stderr,__VA_ARGS__)
#define Debug(x) cout<<#x<<"="<<x<<endl
using namespace std;
typedef long long LL;
const int INF=1e9+7;
inline LL read(){register LL x=0,f=1;register char c=getchar();while(c<48||c>57){if(c=='-')f=-1;c=getchar();}while(c>=48&&c<=57)x=(x<<3)+(x<<1)+(c&15),c=getchar();return f*x;
}const int N=1e6+5;
const int M=2e6+5;struct Graph{struct Edge{int v,nxt;}e[M];int first[N],Ecnt=0;inline void Add_edge(int u,int v){e[++Ecnt]=(Edge){v,first[u]};first[u]=Ecnt;}inline void link(int u,int v){Add_edge(u,v);Add_edge(v,u);}
}G,T;int low[N],dfn[N],st[N],size[N],fa[N],top[N],son[N],dep[N];
int n,m,Q,dft,tp;inline void tarjan(int u){dfn[u]=low[u]=++dft;st[++tp]=u;for(int i=G.first[u];i;i=G.e[i].nxt){int v=G.e[i].v;if(!dfn[v]){tarjan(v);low[u]=min(low[u],low[v]);if(low[v]>=dfn[u]){T.link(++n,u);while(st[tp]!=v) T.link(n,st[tp--]);T.link(n,st[tp--]);}}else low[u]=min(low[u],dfn[v]);}
}inline void dfs1(int u,int pre){dep[u]=dep[pre]+1,fa[u]=pre,size[u]=1;for(int i=T.first[u];i;i=T.e[i].nxt){int v=T.e[i].v;if(v==pre) continue;dfs1(v,u);size[u]+=size[v];if(size[v]>size[son[u]]) son[u]=v;}
}inline void dfs2(int u,int tp){top[u]=tp;if(son[u]){dfs2(son[u],top[u]);}for(int i=T.first[u];i;i=T.e[i].nxt){int v=T.e[i].v;if(v==fa[u]||v==son[u]) continue;dfs2(v,v);}
}inline int LCA(int x,int y){while(top[x]!=top[y]){if(dep[top[x]]<dep[top[y]]) swap(x,y);x=fa[top[x]];}if(dep[x]<dep[y]) return x;return y;
}int main(){n=read(),m=read();for(int i=1;i<=m;i++){int x=read(),y=read();G.link(x,y);}tarjan(1);dfs1(1,0);dfs2(1,1);Q=read();while(Q--){int x=read(),y=read(),p=LCA(x,y);printf("%d\n",(dep[x]+dep[y]-2*dep[p])/2+1);}
}