P1352 没有上司的舞会

P1352

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题目的dfs函数与骑士🔗类似，所以去写了下

代码：

#include<bits/stdc++.h>
using namespace std;

const int N = 6e4 + 7;

int f[N][2], a[N], in[N];

int head[N], tot;
struct Edge{
    int ne, to;
}e[N];

void addedge(int u, int v){
    e[++ tot].ne = head[u];
    e[tot].to = v;
    head[u] = tot;
}

void dfs(int now){
    f[now][0] = 0, f[now][1] = a[now];
    for(int i = head[now]; i ;i = e[i].ne){
        int to = e[i].to;
        dfs(to);
        f[now][0] += max(f[to][0], f[to][1]);
        f[now][1] += f[to][0];
    }
}

int main(){
    int n;
    scanf("%d", &n);
    for(int i = 1;i <= n;i ++) scanf("%d", &a[i]);
    for(int i = 1;i < n;i ++){
        int l, k;
        scanf("%d%d", &l, &k);
        addedge(k, l);
        in[l] ++;
    }
    int rt = 0;
    for(int i = 1;i <= n;i ++)
        if(in[i] == 0){
            rt = i;
            break;
        }
    dfs(rt);
    printf("%d", max(f[rt][0], f[rt][1]));
    return 0;
}