題目：HDU 3078 Network

主要貼一下LCA RMQ的演算法模板，供以後回憶

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <vector>
#include <set>
#include <map>
#include <queue>

using namespace std;

const int maxn = 80005;
int n,q,dfs_clock;
int val[maxn],id[maxn],vs[maxn*2],depth[maxn *2],dp[maxn*2][30],pre[maxn],temp[maxn];
vector <int> g[maxn];
void dfs(int u,int fa,int d)
{
    id[u]=dfs_clock;
    vs[dfs_clock]=u;
    depth[dfs_clock++]=d;
    int len = g[u].size();
    for(int i=0;i<len;i++)
    {
        int v = g[u][i];
        if(v==fa) continue;
        pre[v]=u;
        dfs(v,u,d+1);
        vs[dfs_clock]=u;
        depth[dfs_clock++]=d;
    }
}
void find_depth()
{
    dfs_clock=1;
    memset(id,0,sizeof(id));
    memset(vs,0,sizeof(vs));
    memset(depth,0,sizeof(depth));
    dfs(1,-1,0);
}
void RMQ_init(int n)
{
    for(int i=1;i<=n;i++)
    {
        dp[i][0]=i;
    }
    for(int j=1;(1<<j)<=n;j++)
    {
        for(int i=1;i+(1<<j)-1<=n;i++)
        {
            int a = dp[i][j-1];
            int b = dp[i+(1<<(j-1))][j-1];
            dp[i][j] = depth[a] <= depth[b] ? a:b;
        }
    }
}
int query(int L,int R)
{
    int k=0;
    while((1<<(k+1))<=R-L+1) k++;
    int a = dp[L][k];
    int b = dp[R-(1<<k)+1][k];
    return depth[a]<=depth[b] ? a:b;
}
int LCA(int u,int v)
{
    int x = id[u];
    int y = id[v];
    return x<y? vs[query(x,y)]:vs[query(y,x)];
}
int main()
{
    scanf("%d%d",&n,&q);
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&val[i]);
    }
    for(int i=0;i<=n;i++)
    {
        g[i].clear();
    }
    for(int i=0;i<n-1;i++)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        g[x].push_back(y);
        g[y].push_back(x);
    }
    find_depth();
    RMQ_init(dfs_clock-1);

    for(int i=0;i<q;i++)
    {
        int k,a,b;
        scanf("%d%d%d",&k,&a,&b);
        if(!k)
        {
            val[a]=b;
        }
        else
        {
            int anc = LCA(a,b),cnt=0;
            int cur = a;
            while(cur!=anc)
            {
                temp[cnt++]=val[cur];
                cur = pre[cur];
            }
            cur = b;
            while(cur!=anc)
            {
                temp[cnt++]=val[cur];
                cur = pre[cur];
            }
            temp[cnt++] = val[anc];
            if(cnt < k)
            {
                printf("invalid request!\n");
            }
            else
            {
                sort(temp,temp+cnt,greater<int> ());
                printf("%d\n",temp[k-1]);
            }

        }
    }

    system("pause");
    return 0;
}