[Swust OJ 402]--皇宫看守(树形dp)

 1 #include <iostream>
 2 #include <algorithm>
 3 #include <cstdio>
 4 #include <cstring>
 5 using namespace std;
 6 #define maxn 1510
 7 #define inf 0x3f3f3f3f
 8 typedef long long LL;
 9 
10 int n, x, root, vis[maxn], son[maxn][maxn], cnt[maxn], vi[maxn];
11 LL tmp[maxn], dp[maxn][3];
12 //dp[i][0] i点放看守，dp[i][1] i点不放看守i点被儿子监视，dp[i][2] i点不放看守i点被父节点监视三个情况下的最小费用
13 void tree_dp(int x){
14     if (dp[x][0]) return;
15     for (int i = 1; i <= cnt[x]; i++){
16         int t = son[x][i];
17         tree_dp(t);
18         dp[x][0] += min(dp[t][0], min(dp[t][1], dp[t][2]));
19         dp[x][2] += dp[t][1];
20     }
21     dp[x][0] += vi[x];
22     memset(tmp, 0, sizeof(tmp));
23     LL ptr = 0;
24     for (int i = 1; i <= cnt[x]; i++){
25         int t = son[x][i];
26         tmp[i] = min(dp[t][0], dp[t][1]);
27         ptr += tmp[i];
28     }
29     dp[x][1] = inf;
30     for (int i = 1; i <= cnt[x]; i++){
31         int t = son[x][i];
32         if (ptr - tmp[i] + dp[t][0] < dp[x][1]) dp[x][1] = ptr - tmp[i] + dp[t][0];
33     }
34 }
35 
36 int main(){
37     //freopen("402-皇宫看守.in", "r", stdin);
38     //freopen("402-皇宫看守.out", "w", stdout);
39     while (~scanf("%d", &n)){
40         memset(dp, 0, sizeof(dp));
41         for (int i = 0; i < n; i++){
42             scanf("%d", &x);
43             scanf("%d%d", &vi[x], &cnt[x]);
44             for (int j = 1; j <= cnt[x]; j++){
45                 scanf("%d", &son[x][j]);
46                 vis[son[x][j]] = 1;
47             }
48         }
49         for (int i = 1; i <= n; i++)
50         if (!vis[i]){ root = i; break; }
51         tree_dp(root);
52         printf("%lld\n", min(dp[root][0], dp[root][1]));
53     }
54     return 0;
55 }