牛客练习赛78

B

模拟

#include<bits/stdc++.h>
#define inf 0x3f3f3f3f
#define MAX 1000001
#define inf 0x3f3f3f3f
#define ll long long
#define MAX 1000001
const ll N = 1e5+7;
const ll mod = 1e9+7;
using namespace std;
ll w[N],b[N],ans=0,vis[N],n,m;
int main(){
    scanf("%lld%lld",&n,&m);
    for(int i=1;i<=n;++i)
        scanf("%lld",&w[i]);
    for(int i=1;i<=m;++i){
        scanf("%lld",&b[i]);
        for(int j=1;j<=n;++j)    vis[j]=0;
        for(int j=i-1;j;--j){
            if(b[j]==b[i])    break;
            if(vis[b[j]]==0){
                vis[b[j]]=1;
                ans+=w[b[j]];
            }
        }
    }
    printf("%lld
",ans);
    return 0; 
}

C

树形dp

#include<bits/stdc++.h>
#define inf 1e18
#define ll long long
#define MAX 1000001
const ll N = 2e5+7;
const ll mod = 1e9+7;
using namespace std;
ll n,a[N],s[N],mx[N],ans=-inf;
vector<ll>G[N];
void dfs(int u,int fa){
    ll mx2=-inf;
    s[u]=a[u];mx[u]=-inf;
    for(int i=0;i<G[u].size();++i){
        int v=G[u][i];
        if(v==fa)    continue;
        dfs(v,u);
        s[u]+=s[v];
        if(mx[v]>mx[u]){
            mx2=mx[u],mx[u]=mx[v];
        }
        else if(mx[v]>mx2){
            mx2=mx[v];
        }
    }
    ans=max(ans,mx[u]+mx2);
    mx[u]=max(mx[u],s[u]);
}
int main(){
    scanf("%lld",&n);
    for(int i=1;i<=n;++i)    scanf("%lld",&a[i]);
    for(int i=1;i<n;++i){
        ll u,v;scanf("%lld %lld",&u,&v);
        G[u].push_back(v);
        G[v].push_back(u);
    }
    dfs(1,0);
    if(ans==-inf)    printf("Error
");
    else            printf("%lld
",ans); 
    return 0; 
}