题目
思路
深搜统计深度，倍增( ext{LCA})求边数
(Code)
#include<iostream>
#include<cstring>
#include<string>
#include<cstdio>
#include<algorithm>
#define MAXN 100
#define max_(a,b) a>b?a:b;
using namespace std;
int n,cnt,head[MAXN],dep[MAXN],fa[MAXN][20],lg[MAXN];
int sum1,sum2,ans1,ans2[MAXN];
struct Edge{
int next,to;
}edge[MAXN<<1];
inline int qpow(int a,int b){
int ans=1,base=a;
while(b){
if(b&1) ans*=base;
base*=base;
b>>=1;
}
return ans;
}
inline void addedge(int from,int to){
edge[++cnt].to=to,edge[cnt].next=head[from];
head[from]=cnt;
}
inline int read(){
int x=0;bool f=0;char c=getchar();
while(c<'0'||c>'9'){if(c=='-')f=!f;c=getchar();}
while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}
return f?-x:x;
}
void dfs(int u,int father){
dep[u]=dep[father]+1;
ans2[dep[u]]++;
ans1=max_(ans1,dep[u]);
fa[u][0]=father;
for(int i=head[u];i;i=edge[i].next){
int x=edge[i].to;
if(x!=father) dfs(x,u);
}
}
void lca(int x,int y){
if(dep[x]<dep[y]){
while(dep[y]>dep[x]){
sum2+=qpow(2,lg[dep[y]-dep[x]]-1);
y=fa[y][lg[dep[y]-dep[x]]-1];
}
}else{
while(dep[x]>dep[y]){
sum1+=qpow(2,lg[dep[x]-dep[y]]-1);
x=fa[x][lg[dep[x]-dep[y]]-1];
}
}
if(x==y) return;
for(int k=lg[dep[x]]-1;k>=0;--k){
if(fa[x][k]!=fa[y][k]){
sum1+=qpow(2,k),sum2+=qpow(2,k);
x=fa[x][k],y=fa[y][k];
}
}
sum1++,sum2++;
}
int main(){
n=read();
for(int i=1,u,v;i<n;++i){
u=read(),v=read();
addedge(u,v);
addedge(v,u);
}
dfs(1,0);
for(int i=1;(1<<i)<=n;++i){
for(int j=1;j<=n;++j){
fa[j][i]=fa[fa[j][i-1]][i-1];
}
}
for(int i=1;i<=n;++i){
lg[i]=lg[i-1]+(1<<lg[i-1]==i);
}
int ans=0;
for(int i=1;i<MAXN;++i){
if(ans2[i]>ans){
ans=ans2[i];
}
}
int u,v;
u=read(),v=read();
printf("%d
%d
",ans1,ans);
lca(u,v);
printf("%d
",sum1*2+sum2);
return 0;
}