Hdu 5425 Rikka with Tree II (violent)

Hdu 5425 Rikka with Tree II (violent)

 

 

You can simply enumerate the contribution values when the probability is extremely small.

 

 

#include 
 
  #include 
  
   #include 
   
    #include 
    
     #include 
     
      #include using namespace std;const int maxn = 1e5 + 5;int N, D[maxn];vector
      
        G[maxn];void init () {for (int i = 1; i <= N; i++) G[i].clear();int t;for (int i = 2; i <= N; i++) {scanf(%d, &t);G[t].push_back(i);}queue
       
         Q;D[1] = 0;Q.push(1);while (!Q.empty()) {int u = Q.front();Q.pop();for (int i = 0; i < G[u].size(); i++) {int v = G[u][i];D[v] = D[u] + 1;Q.push(v);}}sort(D + 1, D + 1 + N);}int main () {while (scanf(%d, &N) == 1) {init ();double ans = 0;for (int i = 0; i < N && i < 100; i++) {int u = N - i;double w = 0;for (int j = N; j > u; j--)w += 1.0 * (D[u] + 1) * (D[j] + 1) / (D[u] + D[j] + 2);double t = pow(2, N-u+1) - (N+1) / pow(2, u-1);ans += w / t;}printf(%.6lf, ans);}return 0;}