# zoj 3195 Design the city （lca,dfs+rmq）

Posted by 111qqz on Saturday, May 21, 2016

## TOC

zoj 3195题目链接 题意：求树上三点的最短距离。。。 思路：两两求，和除以2. 因为忘记初始化p=0..WA了将近两个小时。。。？ 妈的智障。

``````/* ***********************************************
Author :111qqz
Created Time :2016年05月21日 星期六 14时44分39秒
File Name :code/zoj/3195.cpp
************************************************ */

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <cmath>
#include <cstdlib>
#include <ctime>
#define fst first
#define sec second
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define ms(a,x) memset(a,x,sizeof(a))
typedef long long LL;
#define pi pair < int ,int >
#define MP make_pair

using namespace std;
const double eps = 1E-8;
const int dx4[4]={1,0,0,-1};
const int dy4[4]={0,-1,1,0};
const int inf = 0x3f3f3f3f;
const int N=5E4+7;
int n,m;
vector < pi > edge[N];
int q;
int in[N];
int E[2*N],R[2*N],dis[N],depth[2*N];
int p;
int dp[2*N][20];
void dfs( int u,int dep,int d,int pre)
{

//  cout<<"u:"<<u<<" dep:"<<dep<<" d:"<<d<<endl;
p++;
E[p] = u;
depth[p] = dep;
R[u] = p ;
dis[u] = d;

int siz = edge[u].size();
for ( int i = 0 ; i < siz ; i++)
{
int v = edge[u][i].fst;
if (v==pre) continue;
dfs(v,dep+1,d+edge[u][i].sec,u);

p++;
E[p] = u;
depth[p] = dep;
}
}

int _min( int l,int r)
{
if (depth[l]<depth[r]) return l;
return r;
}
void rmq_init()
{
for ( int i = 1 ; i <= 2*n+2 ; i++) dp[i][0] = i;

for ( int j = 1 ; (1<<j) <= 2*n+2 ; j++)
for ( int i = 1 ; i + (1<<j)-1 <= 2*n+2 ; i++)
dp[i][j] = _min(dp[i][j-1],dp[i+(1<<(j-1))][j-1]);
}

int rmq_min( int l,int r)
{
if (l>r) swap(l,r);
int k = 0 ;
while (1<<(k+1)<=r-l+1) k++;
return _min(dp[l][k],dp[r-(1<<k)+1][k]);
}
int solve (int x,int y)
{
int LCA = E[rmq_min(R[x],R[y])];
int res = dis[x] + dis[y] - 2 * dis[LCA];
return res;
}
int main()
{
#ifndef  ONLINE_JUDGE
freopen("code/in.txt","r",stdin);
#endif

ms(in,0);
bool ok = false;
while (~scanf("%d",&n)){
if (ok) puts("");
ok = true;
for ( int i = 0 ; i <= n ; i++) edge[i].clear();
for ( int i = 1 ; i <= n-1 ; i++)
{
int u,v,w;
scanf("%d%d%d",&u,&v,&w);
edge[u].push_back(make_pair(v,w));
edge[v].push_back(make_pair(u,w));
}

p = 0 ;
dfs(0,0,0,-1);
rmq_init();

scanf("%d",&q);
while (q--)
{
int x,y,z;
scanf("%d%d%d",&x,&y,&z);
int ans = solve(x,y)+solve(x,z)+solve(y,z);
printf("%d\n",ans/2);
}
}

#ifndef ONLINE_JUDGE
fclose(stdin);
#endif
return 0;
}
``````

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