Luogu P1352 没有上司的舞会

题目描述

https://www.luogu.com.cn/problem/P1352

树形dp入门题

Solution

#include <iostream>
#include <cstdio>
#include <cstring>
#define maxn 6010
using namespace std;

int n, a[maxn];

struct Edge {
    int to, next;
} e[maxn * 2]; int c1, head[maxn];
inline void add_edge(int u, int v) {
    e[c1].to = v; e[c1].next = head[u]; head[u] = c1++;
}

int f[maxn][2]; 
void dfs(int u, int fa) {
    f[u][1] = a[u]; 
    for (int i = head[u]; ~i; i = e[i].next) {
        int v = e[i].to; if (v == fa) continue;
        dfs(v, u);
        f[u][1] += f[v][0];
        f[u][0] += max(f[v][0], f[v][1]);
    }
} 

int main() { memset(head, -1, sizeof head); 
    cin >> n;
    for (int i = 1; i <= n; ++i) cin >> a[i];
    for (int i = 1; i < n; ++i) {
        int x, y; cin >> x >> y;
        add_edge(x, y); add_edge(y, x);
    }
    dfs(1, 0); 
    cout << max(f[1][0], f[1][1]); 
    return 0;
}