分析
https://blog.csdn.net/forever_shi/article/details/88048528
代码
#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<cctype>
#include<cmath>
#include<cstdlib>
#include<ctime>
#include<queue>
#include<vector>
#include<set>
#include<map>
#include<stack>
using namespace std;
#define int long long
const int mod = 1e9+7;
int dp[100100][210],now[210],siz[100100],n,k;
int s[210][210],p[210],res[210];
vector<int>v[100100];
inline void init(){
int i,j;
p[0]=1;
for(i=1;i<=k;i++)p[i]=p[i-1]*i%mod;
s[1][1]=1;
for(i=2;i<=k;i++)
for(j=1;j<=i;j++)
s[i][j]=(s[i-1][j-1]+s[i-1][j]*j%mod)%mod;
}
inline void dfs(int x,int fa){
dp[x][0]=1;
for(int i=0;i<v[x].size();i++){
if(v[x][i]==fa)continue;
dfs(v[x][i],x);
for(int j=0;j<=k;j++)now[j]=dp[x][j];
for(int j=1;j<=k;j++)dp[x][j]=(dp[x][j]+dp[v[x][i]][j]+dp[v[x][i]][j-1])%mod;
dp[x][0]=(dp[x][0]+dp[v[x][i]][0])%mod;
for(int j=0;j<=min(k,siz[x]);j++)
for(int t=0;t<=min(k-j,siz[v[x][i]]);t++){
dp[x][j+t]=(dp[x][j+t]+now[j]*dp[v[x][i]][t]%mod)%mod;
dp[x][j+t+1]=(dp[x][j+t+1]+now[j]*dp[v[x][i]][t]%mod)%mod;
res[j+t]=(res[j+t]+now[j]*dp[v[x][i]][t]%mod)%mod;
res[j+t+1]=(res[j+t+1]+now[j]*dp[v[x][i]][t]%mod)%mod;
}
siz[x]+=siz[v[x][i]]+1;
}
}
signed main(){
int i,j,Ans=0;
scanf("%lld%lld",&n,&k);
for(i=1;i<n;i++){
int x,y;
scanf("%lld%lld",&x,&y);
v[x].push_back(y);
v[y].push_back(x);
}
init();
dfs(1,0);
for(i=1;i<=k;i++)
Ans=(Ans+p[i]*s[k][i]%mod*res[i]%mod)%mod;
cout<<Ans;
return 0;
}