[HNOI2003]消防局的设立

 1 #include<cstdio>
 2 #include<vector>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<functional>
 6 const int N=1001;
 7 int p[N];
 8 bool safe[N]={0};
 9 std::vector<int> c[N];
10 struct Vertex {
11     int id,depth;
12     bool operator > (const Vertex &x) const {
13         return this->depth>x.depth;
14     }
15 };
16 Vertex v[N];
17 void dfs(const int x,const int depth) {
18     v[x].depth=depth;
19     for(unsigned int i=0;i<c[x].size();i++) dfs(c[x][i],depth+1);
20 }
21 void update(const int x) {
22     safe[p[x]]=safe[p[p[x]]]=true;
23     for(unsigned int i=0;i<c[p[x]].size();i++) safe[c[p[x]][i]]=true;
24     for(unsigned int i=0;i<c[x].size();i++) {
25         safe[c[x][i]]=true;
26         for(unsigned int j=0;j<c[c[x][i]].size();j++) {
27             safe[c[c[x][i]][j]]=true;
28         }
29     }
30 }
31 int main() {
32     int n;
33     scanf("%d",&n);
34     p[1]=1;
35     v[1].id=1;
36     for(int i=2;i<=n;i++) {
37         v[i].id=i;
38         scanf("%d",&p[i]);
39         c[p[i]].push_back(i);
40     }
41     dfs(1,0);
42     std::sort(&v[1],&v[n+1],std::greater<Vertex>());
43     int ans=0;
44     for(int i=1;i<=n;i++) {
45         if(safe[v[i].id]) continue;
46         update(p[p[v[i].id]]);
47         ans++;
48     }
49     printf("%d\n",ans);
50     return 0;
51 }