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;

}