CCA的子树

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code

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll N = 1e5+5;
const ll INF = 1e18;
ll n, val[N], sum[N], mx[N], ans = -INF;
/*sum[i]保存以结点i为根的树的权值和，mx[i]保存以结点i为根的子树的最大权值和*/
vector<ll> vec[N];
void dfs(ll x, ll fa)
{
    ll maxn = -INF;
    sum[x] = val[x];
    for(ll i = 0; i < vec[x].size(); i++)
    {
        ll y = vec[x][i];
        if(y == fa) continue;
        dfs(y, x);
        sum[x] += sum[y];
        if(maxn != -INF)
            ans = max(ans, maxn + mx[y]);
        maxn = max(maxn, mx[y]);//maxn保存以x为根的子树的最大权值和
    }
    mx[x] = max(maxn, sum[x]);
}
int main()
{
    cin >> n;
    for(ll i = 1; i <= n; i++)
        cin >> val[i];
    for(ll i = 1; i < n; i++)
    {
        ll u, v;
        cin >> u >> v;
        vec[u].push_back(v);
        vec[v].push_back(u);
    }
    dfs(1, 0);
    if (ans == -INF) 
        printf("Error\n");
    else 
        printf("%lld\n", ans);
    return 0;
}