Submission #5543135
Source Code Expand
#include<bits/stdc++.h>
using namespace std;
#define fs first
#define sc second
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define ALL(A) A.begin(),A.end()
#define RALL(A) A.rbegin(),A.rend()
typedef long long LL;
typedef pair<LL,LL> P;
const LL mod=1000000007;
const LL LINF=1LL<<60;
const int INF=1<<30;
int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};
vector<LL> fact;
vector<LL> inver(200001);
vector<int> v[1001];
LL combi(int n,int r){
if(n<r||n<0||r<0) return 0;
return fact[n]%mod*inver[n-r]%mod*inver[r]%mod;
}
LL fpow(LL a, LL n){
LL x = 1;
while(n > 0){
if(n&1){
x=x*a%mod;
}
a=a*a%mod;
n >>= 1;
}
return x;
}
void set_combi(){
LL s=1;
fact.push_back(1);
for(int i=1;i<=200000;i++){
s*=i;
s%=mod;
fact.push_back(s);
}
inver[200000]=fpow(fact[200000],mod-2);
for(int i=199999;i>=0;i--){
inver[i]=inver[i+1]*(i+1)%mod;
}
}
vector<P> dp1(1001,mp(-1,-1));
vector<P> dp2(1001,mp(-1,-1));
int n;
P dfs(int u,int prev){
if(dp1[u]!=P(-1,-1)) return dp1[u];
P ret = mp(1,0);
for (int i = 0; i < v[u].size(); i++) {
if(v[u][i]==prev) continue;
P p = dfs(v[u][i],u);
ret.sc += p.sc;
ret.fs = ret.fs*combi(ret.sc,p.sc)%mod*p.fs%mod;
}
ret.sc++;
return dp1[u] = ret;
}
void dfs2(int u,int prev,LL st,LL t){
dp2[u] = mp(st,t);
for (int i = 0; i < v[u].size(); i++) {
if(v[u][i]==prev) continue;
dp2[u].sc += dp1[v[u][i]].sc;
dp2[u].fs = dp2[u].fs*combi(dp2[u].sc,dp1[v[u][i]].sc)%mod*dp1[v[u][i]].fs%mod;
}
for (int i = 0; i < v[u].size(); i++) {
if(v[u][i]==prev) continue;
dfs2(v[u][i],u,dp2[u].fs*fpow(dp1[v[u][i]].fs*combi(dp2[u].sc,dp1[v[u][i]].sc),mod-2)%mod,n-dp1[v[u][i]].sc);
}
}
int main(){
set_combi();
cin >> n;
for (int i = 0; i < n-1; i++) {
int x,y;cin >> x >> y;
x--,y--;
v[x].pb(y);
v[y].pb(x);
}
dfs(0,-1);
dfs2(0,-1,1,0);
LL ans = 0;
for (int i = 0; i < n; i++) {
ans = (ans + dp2[i].fs)%mod;
}
cout << ans*inver[2]%mod << endl;
return 0;
}
Submission Info
Submission Time |
|
Task |
N - 木 |
User |
Yukly |
Language |
C++14 (GCC 5.4.1) |
Score |
0 |
Code Size |
2323 Byte |
Status |
WA |
Exec Time |
7 ms |
Memory |
4088 KB |
Judge Result
Set Name |
All |
Score / Max Score |
0 / 5 |
Status |
|
Set Name |
Test Cases |
All |
00, 01, 02, 03, 04, 05, 06, 90, 91 |
Case Name |
Status |
Exec Time |
Memory |
00 |
AC |
7 ms |
4088 KB |
01 |
AC |
7 ms |
4088 KB |
02 |
WA |
7 ms |
4088 KB |
03 |
WA |
7 ms |
4088 KB |
04 |
WA |
7 ms |
4088 KB |
05 |
WA |
7 ms |
4088 KB |
06 |
WA |
7 ms |
4088 KB |
90 |
AC |
6 ms |
4088 KB |
91 |
AC |
6 ms |
4088 KB |