题目链接

题意：







题解：



















AC代码

/*
    Author:zzugzx
    Lang:C++
    Blog:blog.csdn.net/qq_43756519
*/
#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define endl '\n'
#define SZ(x) (int)x.size()
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int mod=1e9+7;
//const int mod=998244353;
const double eps = 1e-10;
const double pi=acos(-1.0);
const int maxn=1e6+10;
const ll inf=0x3f3f3f3f;
const int dir[][2]={{0,1},{1,0},{0,-1},{-1,0},{1,1},{1,-1},{-1,1},{-1,-1}};

ll ans,n,p,lim;
vector<int> g[maxn];
ll s1[maxn],s2[maxn],s[maxn],cnt[maxn],a[maxn],tot[maxn];
void dfs(int u,int fa,ll d){
    if(d>lim){
        ll t=d-lim;
        s[u]-=cnt[t];
        s1[u]-=cnt[t]*t;
        s2[u]-=cnt[t]*t*t;
    }
    ll tmp=s[u]*(p-d*d)-s2[u]+2*d*s1[u];
    if(a[u]>=tmp)tot[u]=(a[u]-tmp)/p+1,ans+=tot[u];
    cnt[d]=tot[u];
    for(auto v:g[u]){
        if(v==fa)continue;
        s[v]=s[u]+tot[u];
        s1[v]=s1[u]+tot[u]*d;
        s2[v]=s2[u]+tot[u]*d*d;
        dfs(v,u,d+1);
    }
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    cin>>n>>p;lim=sqrt(p-1)+1;
    for(int i=1;i<=n;i++)cin>>a[i];
    for(int i=1;i<n;i++){
        int u,v;
        cin>>u>>v;
        g[u].pb(v);
        g[v].pb(u);
    }
    dfs(1,0,1);
    cout<<ans;
    return 0;
}