luogu P1315 联合权值 枚举

#include <cstdio>
#include <algorithm>
using namespace std;
typedef long long ll;
const int N = 200100,M = 400100,mo = 10007;//用变量方便更改 
int cnt,n,maxn;
ll ans;
int w[N],head[N],to[M],nxt[M];
void add(int x,int y)
{
    nxt[++cnt] = head[x];
    to[cnt] = y;
    head[x] = cnt;
}
void dfs(int x,int fa)
{
    ll sum = 0;
    int max1 = 0,max2 = 0;
    for (int i = head[x];i;i = nxt[i])
    {
        sum += w[to[i]];
        if (w[to[i]] > max1)//赋值顺序一定要考虑清楚 
        {
            max2 = max1;
            max1 = w[to[i]];
        }else if (w[to[i]] > max2)//一定要写else，否则？ 
            max2 = w[to[i]];
    }
    maxn = max(maxn,max1 * max2);
    for (int i = head[x];i;i = nxt[i])
    {
        ans += (sum - w[to[i]]) * w[to[i]];
        ans %= mo;
    }
    for (int i = head[x];i;i = nxt[i])
        if (to[i] != fa)
            dfs(to[i],x);
}
int main()
{
    scanf("%d",&n);
    int u,v;
    for (int i = 1;i <= n - 1;i++)
    {
        scanf("%d%d",&u,&v); 
        add(u,v);
        add(v,u);
    }
    for (int i = 1;i <= n;i++)
        scanf("%d",&w[i]);
    dfs(1,0);
    printf("%d %lld
",maxn,ans); 
    return 0;
}