poj 1330 Nearest Common Ancestors 裸的LCA

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#define N 10010
using namespace std;
int dep[N],farther[N],vi[N],sec[N],Md,index[N],e,set[N];
struct Edge{
    int to,next;
}edge[N];
void addedge(int from,int to)
{
    edge[e].to=to;
    edge[e].next=index[from];
    index[from]=e++;
}
void dfs(int u)
{
    int i,now;
    for(i=index[u];i!=-1;i=edge[i].next)
    {
        now=edge[i].to;
        dep[now]=dep[u]+1;
        farther[now]=u;
        dfs(now);
    }
    Md=max(Md,dep[u]);
}
void make_sec(int u,int Sec)
{
    int i,now;//cout<<u<<" "<<Sec<<endl;
    if(dep[u]<Sec)
        sec[u]=0;
    else
    {
        if(dep[u]%Sec==0)
            sec[u]=farther[u];
        else
            sec[u]=sec[farther[u]];
    }
    for(i=index[u];i!=-1;i=edge[i].next)
    {
        now=edge[i].to;
        make_sec(now,Sec);
    }
    
}
int LCA(int a,int b)
{
    while(sec[a]!=sec[b])
    {
        if(dep[a]>dep[b])
            a=sec[a];
        else
            b=sec[b];
    }
    while(a!=b)
    {
        if(dep[a]>dep[b])
            a=farther[a];
        else
            b=farther[b];
    }
    return a;
}
int find(int x)
{
    if(x!=set[x])
        set[x]=find(set[x]);
    return set[x];
}
void merg(int a,int b)
{
    int x,y;
    x=find(a);
    y=find(b);
    set[y]=x;
}
void init()
{
    e=0;
    memset(dep,0,sizeof(dep));
    memset(sec,0,sizeof(sec));
    memset(index,-1,sizeof(index));
    memset(farther,0,sizeof(farther));
    for(int i=0;i<=N;i++)
        set[i]=i;
}
int main()
{
    int t,i,j,a,b,n;
    scanf("%d",&t);
    while(t--)
    {
        init();
        scanf("%d",&n);
        for(i=0;i<n-1;i++)
        {
            scanf("%d%d",&a,&b);
            merg(a,b);
            addedge(a,b);
        }
        scanf("%d%d",&a,&b);
        dfs(find(1));
        make_sec(find(1),sqrt(1.0*Md));//cout<<"ok"<<endl;
        printf("%d\n",LCA(a,b));
    }
    return 0;
}