题目链接 AcWing 285. 没有上司的舞会
思路 (求和公式不好打 直接截的书上的)
C++代码
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 6010;
int n;
int f[N][2];
int happy[N];
int h[N], e[N], ne[N], idx;
bool has_fa[N];
void add(int a, int b)
{
e[idx] = b, ne[idx] = h[a], h[a] = idx ++;
}
void dfs(int u)
{
f[u][1] = happy[u]; //选择第u个节点
for (int i = h[u]; i != -1; i = ne[i])
{
int j = e[i];
dfs(j);
//状态转移
f[u][1] += f[j][0];
f[u][0] += max(f[j][0], f[j][1]);
}
}
int main()
{
cin >> n;
for (int i = 1; i <= n; i ++ ) cin >> happy[i];
memset(h, -1, sizeof h);
for (int i = 1; i < n; i ++ )
{
int a, b;
cin >> a >> b;
has_fa[a] = true;
add(b, a);
}
int root = 1;
while (has_fa[root]) root ++; //寻找根节点
dfs(root);
cout << max(f[root][1], f[root][0]) << endl;
return 0;
}