bzoj 1040 基向内环树dp

#include<bits/stdc++.h>
#define LL long long
#define fi first
#define se second
#define mk make_pair
#define pii pair<int, int>
#define y1 skldjfskldjg
#define y2 skldfjsklejg
 
using namespace std;
 
const int N = 1e6 + ;
const int M = 1e5 + ;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9 +;
 
int n, tot, a[N], fa[N], b[N], head[N];
bool vis[N];
LL f[N][];
 
struct Edge {
    int to, nx;
} edge[N << ];
 
void add(int u, int v) {
    edge[tot].to = v;
    edge[tot].nx = head[u];
    head[u] = tot++;
}
 
int getRoot(int x) {
    return fa[x] == x ? x : fa[x] = getRoot(fa[x]);
}
 
void dp(int u, int fa, int ban) {
    f[u][] = , f[u][] = a[u];
    LL tmp[] = {};
 
    for(int i = head[u]; ~i; i = edge[i].nx) {
        int v = edge[i].to;
        if(v == fa || i == ban || (i ^ ) == ban) continue;
        dp(v, u, ban);
 
        tmp[] = f[u][], tmp[] = f[u][];
 
        tmp[] = max(tmp[], f[u][] + f[v][]);
        tmp[] = max(tmp[], f[u][] + f[v][]);
        tmp[] = max(tmp[], f[u][] + f[v][]);
 
        f[u][] = tmp[], f[u][] = tmp[];
    }
}
 
int main() {
    memset(head, -, sizeof(head));
 
    scanf("%d", &n);
    for(int i = ; i <= n; i++) {
        scanf("%d%d", &a[i], &b[i]);
        add(i, b[i]); add(b[i], i);
        fa[i] = i;
    }
 
    LL ans = ;
    for(int i = ; i <= n; i++) {
        int x = getRoot(i);
        int y = getRoot(b[i]);
        if(x != y) {
            fa[x] = y;
        } else {
            LL ret = ;
            dp(i, , i *  - );
            ret = max(ret, f[i][]);
            dp(b[i], , i *  - );
            ret = max(ret, f[b[i]][]);
            ans += ret;
        }
    }
 
    printf("%lld\n", ans);
    return ;
}
 
/*
*/