校赛4395: 大家 倍增

4395: 大家

这个题目和lca类似，就是要计算两个点间所有点的最大权值点。

可以在更新祖先的时候更新最大值。

（记得多组输入

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <cstdlib>
#include <iterator>
#include <cmath>
#include <iomanip>
#include <bitset>
#include <cctype>
using namespace std;

#define lson (l , mid , rt << 1)
#define rson (mid + 1 , r , rt << 1 | 1)
#define debug(x) cerr << #x << " = " << x << "\n";
#define pb push_back
#define pq priority_queue
#pragma comment(linker, "/STACK:10240000000,10240000000")//扩栈，要用c++交，用g++交并没有什么卵用。。
typedef long long ll;
typedef unsigned long long ull;

typedef pair<ll ,ll > pll;
typedef pair<int ,int > pii;

#define fi first
#define se second

#define OKC ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define FT(A,B,C) for(int A=B;A <= C;++A)  //用来压行
#define REP(i , j , k)  for(int i = j ; i <  k ; ++i)


const ll mos = 0x7FFFFFFF;  //2147483647
const ll nmos = 0x80000000;  //-2147483648

template<typename T>
inline T read(T&x){
    x=0;int f=0;char ch=getchar();
    while (ch<'0'||ch>'9') f|=(ch=='-'),ch=getchar();
    while (ch>='0'&&ch<='9') x=x*10+ch-'0',ch=getchar();
    return x=f?-x:x;
}
// #define _DEBUG;         //*//
#ifdef _DEBUG
freopen("input", "r", stdin);
// freopen("output.txt", "w", stdout);
#endif
///*-----------------show time----------------*/
            const int maxn = 20009;
            vector<int>mp[maxn];
            int n,m;
            int anc[maxn][30];
            int maxv[maxn][30],a[maxn];
            int fa[maxn];
            int deep[maxn];

            void dfs(int x){
                anc[x][0] = fa[x];
                maxv[x][0] = max(a[fa[x]],a[x]);
                for(int i=1; i<=22; i++){
                    anc[x][i] = anc[anc[x][i-1]][i-1];
                    maxv[x][i] = max( maxv[x][i-1],  maxv[anc[x][i-1]][i-1]);
                }

                for(int i=0; i<mp[x].size(); i++){
                        int u = mp[x][i];
                        if(u==fa[x])continue;
                        fa[u] = x;
                        deep[u] = deep[x] + 1;
                        dfs(u);
                }

            }
int main(){
            while(~scanf("%d%d", &n, &m)){

                for(int i=1; i<=n; i++)mp[i].clear();
                memset(deep,0,sizeof(deep));
                memset(fa,-1,sizeof(fa));
                memset(anc,0,sizeof(anc));
                memset(maxv, 0, sizeof(maxv));
                for(int i=1; i<n; i++){
                    int u,v;
                    scanf("%d%d", &u, &v);
                    mp[u].pb(v);
                    mp[v].pb(u);
                }

                for(int i=1; i<=n; i++){
                    scanf("%d", &a[i]);
                }
                fa[1] = 0;
                deep[1] = 1;
                dfs(1);

                for(int i=1; i<=m; i++){
                        int u,v;
                        scanf("%d%d", &u, &v);

                        if(u==v){
                            printf("%d\n",a[u]);
                            continue;
                        }

                        if(deep[u] >= deep[v]){
                            swap(u,v);
                        }

                        int mx = max(a[v] , a[u]);
                        for(int j=22; j>=0; j--){

                            if(deep[u] <= deep[anc[v][j]])
                            {
                                    mx = max(mx,maxv[v][j]);
                                    v = anc[v][j];

                            }
                        }

                        if(u==v){
                                printf("%d\n",mx);

                        } else
                            printf("-1\n");
                }
            }
    return 0;
}