POJ 3728

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <cmath>
#include <utility>
#include <vector>
#include <queue>
#include <map>
#include <set>
#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)>(y)?(y):(x))

using namespace std;

long long maxp[50005],minp[50005],up[50005],down[50005];
int be[50005],all;
int bq[50005],qall;
long long question[50005][3];
int f[50005];
bool vis[50005];
int x,y,n,q;

struct Edge{
    int y,ne;
}e[150005];
struct Query{
    int y,res,ne;
}query[150005];
vector<int> num[50005];

void add(int x, int y)
{
    e[all].y=y;
    e[all].ne=be[x];
    be[x]=all++;

    e[all].y=x;
    e[all].ne=be[y];
    be[y]=all++;
}
void qadd(int x, int y, int i)
{
    query[qall].y=y;
    query[qall].res=i;
    query[qall].ne=bq[x];
    bq[x]=qall++;

    query[qall].y=x;
    query[qall].res=i;
    query[qall].ne=bq[y];
    bq[y]=qall++;
}

int find(int x)
{
    int oldf=f[x];
    if(f[x]!=x) f[x]=find(f[x]);
    up[x]=max(max(up[x],up[oldf]),maxp[oldf]-minp[x]);
    down[x]=max(max(down[x],down[oldf]),maxp[x]-minp[oldf]);
    maxp[x]=max(maxp[oldf],maxp[x]);
    minp[x]=min(minp[oldf],minp[x]);
    return f[x];
}

void tarjan(int u)
{
    vis[u]=1;
    for(int i=be[u]; i!=-1; i=e[i].ne)
    {
        int v=e[i].y;
        if(!vis[v])
        {
            tarjan(v);
            f[v]=u;
        }
    }

    for(int i=bq[u]; i!=-1; i=query[i].ne)
        if(vis[query[i].y])
        {
            int fx=find(query[i].y);
            num[fx].push_back(query[i].res);
        }

    for(vector<int>::iterator it=num[u].begin(); it!=num[u].end(); it++)
    {
        int x=question[*it][0], y=question[*it][1];
        find(x);
        find(y);
        question[*it][2]=max(max(up[x],down[y]),maxp[y]-minp[x]);
    }
}

int main()
{
    scanf("%d",&n);
    for(int i=1; i<=n; i++)
    {
        scanf("%d",&x);
        minp[i]=maxp[i]=x;
        up[i]=down[i]=0;
        f[i]=i;
    }
    memset(be,-1,sizeof(be));
    memset(bq,-1,sizeof(bq));
    all=qall=0;
    memset(vis,0,sizeof(vis));

    for(int i=1; i<=n-1; i++)
    {
        scanf("%d%d",&x,&y);
        add(x,y);
    }

    scanf("%d",&q);
    for(int i=1; i<=q; i++)
    {
        scanf("%d%d",&x,&y);
        qadd(x,y,i);
        question[i][0]=x;
        question[i][1]=y;
        question[i][2]=0;
    }

    tarjan(1);

    for(int i=1; i<=q; i++)
        printf("%d\n",question[i][2]);

    return 0;
}