bzoj1787

题目:http://www.lydsy.com/JudgeOnline/problem.php?id=1787

刚开始好像很难的样子

画了一下，发现好像只有3种情况，且最终的P点一定是两两LCA中的一个。

裸的LCA

怪不得数据那么大

#include<cstdio>

#include<cstdlib>

#include<iostream>

#include<fstream>

#include<algorithm>

#include<cstring>

#include<string>

#include<cmath>

#include<queue>

#include<stack>

#include<map>

#include<utility>

#include<set>

#include<bitset>

#include<vector>

#include<functional>

#include<deque>

#include<cctype>

#include<climits>

#include<complex>

//#include<bits/stdc++.h>适用于CF,UOJ，但不适用于poj

 

using namespace std;



typedef long long LL;

typedef double DB;

typedef pair<int,int> PII;

typedef complex<DB> CP;



#define mmst(a,v) memset(a,v,sizeof(a))

#define mmcy(a,b) memcpy(a,b,sizeof(a))

#define re(i,a,b)  for(i=a;i<=b;i++)

#define red(i,a,b) for(i=a;i>=b;i--)

#define fi first

#define se second

#define m_p(a,b) make_pair(a,b)

#define SF scanf

#define PF printf

#define two(k) (1<<(k))



template<class T>inline T sqr(T x){return x*x;}

template<class T>inline void upmin(T &t,T tmp){if(t>tmp)t=tmp;}

template<class T>inline void upmax(T &t,T tmp){if(t<tmp)t=tmp;}



const DB EPS=1e-9;

inline int sgn(DB x){if(abs(x)<EPS)return 0;return(x>0)?1:-1;}

const DB Pi=acos(-1.0);



inline int gint()

  {

        int res=0;bool neg=0;char z;

        for(z=getchar();z!=EOF && z!='-' && !isdigit(z);z=getchar());

        if(z==EOF)return 0;

        if(z=='-'){neg=1;z=getchar();}

        for(;z!=EOF && isdigit(z);res=res*10+z-'0',z=getchar());

        return (neg)?-res:res; 

    }

inline LL gll()

  {

      LL res=0;bool neg=0;char z;

        for(z=getchar();z!=EOF && z!='-' && !isdigit(z);z=getchar());

        if(z==EOF)return 0;

        if(z=='-'){neg=1;z=getchar();}

        for(;z!=EOF && isdigit(z);res=res*10+z-'0',z=getchar());

        return (neg)?-res:res; 

    }



const int maxN=500000;

const int maxM=500000;



int N,M;

int now,first[maxN+100];

struct Tedge{int v,next;}edge[2*maxN+100];

int fa[maxN+100],dep[maxN+100],jump[maxN+100][40];



inline void addedge(int u,int v)

  {

      now++;

      edge[now].v=v;

      edge[now].next=first[u];

      first[u]=now;

  }



int head,tail,que[maxN+100];

inline void BFS()

  {

      int i,j;

      dep[que[head=tail=1]=1]=1;

      fa[1]=1;

      while(head<=tail)

        {

            int u=que[head++],v;

            for(i=first[u],v=edge[i].v;i!=-1;i=edge[i].next,v=edge[i].v)if(!dep[v]) dep[que[++tail]=v]=dep[u]+1,fa[v]=u;

        }

      re(j,1,tail)

        {

            int u=que[j];

            jump[u][0]=fa[u];

            re(i,1,30)jump[u][i]=jump[jump[u][i-1]][i-1];

        }

  }



inline void swim(int &x,int H){for(int i=0;H!=0;H>>=1,i++)if(H&1)x=jump[x][i];}

inline int lca(int x,int y)

  {

      if(dep[x]<dep[y]) swap(x,y);

      swim(x,dep[x]-dep[y]);

      if(x==y)return x;

      int i;red(i,30,0)if(jump[x][i]!=jump[y][i])x=jump[x][i],y=jump[y][i];

      return jump[x][0];

  }



inline int dist(int a,int b){return dep[a]+dep[b]-2*dep[lca(a,b)];}



int main()

  {

      freopen("bzoj1787.in","r",stdin);

      freopen("bzoj1787.out","w",stdout);

      int i;

      N=gint();M=gint();

      mmst(first,-1);now=-1;

      re(i,1,N-1){int x=gint(),y=gint();addedge(x,y);addedge(y,x);}

      BFS();

      while(M--)

        {

            int a=gint(),b=gint(),c=gint(),p,cost,ansp,anscost;

            ansp=lca(a,b);anscost=dist(a,ansp)+dist(b,ansp)+dist(c,ansp);

            p=lca(a,c);cost=dist(a,p)+dist(b,p)+dist(c,p);if(cost<anscost){anscost=cost;ansp=p;}

            p=lca(b,c);cost=dist(a,p)+dist(b,p)+dist(c,p);if(cost<anscost){anscost=cost;ansp=p;}

            PF("%d %d\n",ansp,anscost);

        }

      return 0;

  }

            

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