poj 2342 树形dp

//再水一发树形dp
 1 #include "iostream"
 2 #include "cstdio"
 3 #include "cstring"
 4 #include "algorithm"
 5 using namespace std;
 6 int dp[6010][2];
 7 bool vis[6010];
 8 int tot, first[6010], next[6010], to[6010];
 9 int n, ans[6010];
10 void dfs(int root)
11 {
12     vis[root] = 1;
13     dp[root][1] = ans[root];
14     int edge;
15     for(edge = first[root]; edge; edge = next[edge]) {
16         dfs(to[edge]);
17         dp[root][0] += max(dp[to[edge]][0], dp[to[edge]][1]);
18         dp[root][1] += dp[to[edge]][0];
19     }
20 }
21 
22 int main()
23 {
24     int i;
25     scanf("%d", &n);
26     for(i = 1; i <= n; ++i)
27         scanf("%d", &ans[i]);
28     int b, a;
29     tot = 0;
30     int root = n * (n + 1);
31     root >>= 1;
32     while(scanf("%d%d", &b, &a) && (a || b)) {
33         next[++tot] = first[a];
34         first[a] = tot;
35         to[tot] = b;
36         root -= b;
37     }
38     dfs(root);
39     printf("%d
", max(dp[root][0], dp[root][1]));
40 }