Bear and Destroying Subtrees
看了很久，稍微理解了一点．．．
代码转自czk
dp[v][h]表示以v为祖先的子树最大高度为h时的概率
1 #include <iostream> 2 #include <cstdio> 3 #include <vector> 4 #include <cstring> 5 #include <cmath> 6 #include <ctime> 7 using namespace std; 8 9 10 #define N 500020 11 #define T 66 12 #define eps 1e-8 13 14 int n; 15 double dp[N][T]; 16 int fa[N], d[N]; 17 18 19 int main() { 20 freopen("in.txt", "r", stdin); 21 int q; 22 scanf("%d", &q); 23 n = 1; 24 for(int i = 0; i < T; ++i) dp[1][i] = 1; 25 26 while(q--) { 27 int t, v; 28 scanf("%d%d", &t, &v); 29 if(t == 1) { 30 ++n; 31 for(int i = 0; i < T; ++i) dp[n][i] = 1; 32 fa[n] = v; 33 d[v]++; 34 double pre = dp[v][0]; 35 36 dp[v][0] = pow(0.5, d[v]); 37 int k = 1; 38 while(fa[v] && k < T) { 39 int u = fa[v]; 40 double tmp = dp[u][k]; 41 dp[u][k] /= 0.5 + 0.5 * pre; 42 dp[u][k] *= 0.5 + 0.5 * dp[v][k-1]; 43 pre = tmp; 44 v = u; 45 ++k; 46 } 47 } 48 else { 49 double ans = 0; 50 for(int i = 1; i < T; ++i) ans += i * (dp[v][i] - dp[v][i-1]); 51 printf("%.12lf ", ans); 52 } 53 } 54 return 0; 55 }