Submission #2375087
Source Code Expand
#include<bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,n) for(int i=0;i<(n);i++)
#define pb push_back
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;
template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}
const int mod=1000000007;
inline void add(int &a,int b){
a+=b;
if(a>=mod)a-=mod;
}
int mpow(int n,int m){
int ret=1;
while(m){
if(m&1)ret=ret*n%mod;
n=n*n%mod;
m>>=1;
}
return ret;
}
const int FACT_SIZE=1111111;
int fact[FACT_SIZE];
int inv[FACT_SIZE];
struct fact_exec{
fact_exec(){
fact[0]=1;
for(int i=1;i<FACT_SIZE;i++)fact[i]=fact[i-1]*i%mod;
inv[FACT_SIZE-1]=mpow(fact[FACT_SIZE-1],mod-2);
for(int i=FACT_SIZE-2;i>=0;i--)inv[i]=inv[i+1]*(i+1)%mod;
}
}factexec;
int nCk(int n,int k){
if(n<0|k<0||k>n)return 0;
return fact[n]*inv[k]%mod*inv[n-k]%mod;
}
int nPk(int n,int k){
if(n<0||k<0||k>n)return 0;
return fact[n]*inv[n-k]%mod;
}
int N;
vint G[1111];
int dist[1111];
void dfs(int v,int p,int d){
dist[v]=d;
for(auto u:G[v]){
if(u==p)continue;
dfs(u,v,d+1);
}
}
int D;
int X;
int dp[1111][1111];
void dfs2(int v,int p,int d){
int l=max(0ll,X+d-D/2);
for(int i=l;i<=X;i++)dp[v][i]=1;
for(auto u:G[v]){
if(u==p)continue;
dfs2(u,v,d+1);
for(int i=l;i<=X;i++)dp[v][i]=dp[v][i]*(dp[u][i]+dp[u][i+1])%mod;
}
}
void solve(int c){
int ans=0;
for(X=0;X<=D/2;X++){
memset(dp,0,sizeof(dp));
dfs2(c,-1,0);
add(ans,dp[c][0]);
}
cout<<ans<<endl;
}
signed main(){
cin>>N;
rep(i,N-1){
int a,b;
cin>>a>>b;
a--;b--;
G[a].pb(b);G[b].pb(a);
}
dfs(0,-1,0);
int v=0;
rep(i,N)if(dist[i]>dist[v])v=i;
dfs(v,-1,0);
int u=0;
rep(i,N)if(dist[i]>dist[u])u=i;
vint latte(N);
rep(i,N)latte[i]=dist[i];
dfs(u,-1,0);
rep(i,N)chmax(latte[i],dist[i]);
vint lis;
rep(i,N)if(latte[i]<=(dist[v]+1)/2)lis.pb(i);
D=dist[v];
if(lis.size()==1){
solve(lis[0]);
}
else{
int u=lis[0],v=lis[1];
vint x(N),y(N),z(N),w(N);
for(X=0;X<=D/2;X++){
memset(dp,0,sizeof(dp));
dfs2(u,v,0);
x[X]=dp[u][0];
memset(dp,0,sizeof(dp));
dfs2(v,u,0);
y[X]=dp[v][0];
}
D++;
for(X=0;X<=D/2;X++){
memset(dp,0,sizeof(dp));
dfs2(u,v,0);
z[X]=dp[u][0];
memset(dp,0,sizeof(dp));
dfs2(v,u,0);
w[X]=dp[v][0];
}
D--;
z[0]=w[0]=0;
for(int i=1;i<N;i++)z[i]=(z[i]-x[i]-x[i-1]+mod*2)%mod;
for(int i=1;i<N;i++)w[i]=(w[i]-y[i]-y[i-1]+mod*2)%mod;
int ans=0;
for(int i=0;i<=D/2;i++){
for(int j=0;j<=D/2;j++){
int a=i;
int b=D/2-i;
int c=j;
int d=D/2-j;
if(a+d<=D/2+1&&b+c+1<=D/2+1)add(ans,x[i]*y[j]%mod);
if(a+d+1<=D/2+1&&b+c<=D/2+1)add(ans,x[i]*y[j]%mod);
}
}
for(int i=0;i<=D/2;i++){
for(int j=0;j<=D/2+1;j++){
int a=i;
int b=D/2-i;
int c=j;
int d=D/2+1-j;
if(a+d<=D/2+1&&b+c+1<=D/2+1)add(ans,x[i]*w[j]%mod);
if(a+d+1<=D/2+1&&b+c<=D/2+1)add(ans,x[i]*w[j]%mod);
}
}
for(int i=0;i<=D/2+1;i++){
for(int j=0;j<=D/2+1;j++){
int a=i;
int b=D/2+1-i;
int c=j;
int d=D/2+1-j;
if(a+d<=D/2+1&&b+c+1<=D/2+1)add(ans,z[i]*w[j]%mod);
if(a+d+1<=D/2+1&&b+c<=D/2+1)add(ans,z[i]*w[j]%mod);
}
}
for(int i=0;i<=D/2+1;i++){
for(int j=0;j<=D/2;j++){
int a=i;
int b=D/2+1-i;
int c=j;
int d=D/2-j;
if(a+d<=D/2+1&&b+c+1<=D/2+1)add(ans,z[i]*y[j]%mod);
if(a+d+1<=D/2+1&&b+c<=D/2+1)add(ans,z[i]*y[j]%mod);
}
}
cout<<ans<<endl;
}
return 0;
}
Submission Info
Submission Time |
|
Task |
D - Oriented Tree |
User |
latte0119 |
Language |
C++14 (GCC 5.4.1) |
Score |
1800 |
Code Size |
4635 Byte |
Status |
AC |
Exec Time |
1439 ms |
Memory |
27392 KB |
Judge Result
Set Name |
Sample |
All |
Score / Max Score |
0 / 0 |
1800 / 1800 |
Status |
|
|
Set Name |
Test Cases |
Sample |
0_00.txt, 0_01.txt, 0_02.txt, 0_03.txt |
All |
0_00.txt, 0_01.txt, 0_02.txt, 0_03.txt, 1_00.txt, 1_01.txt, 1_02.txt, 1_03.txt, 1_04.txt, 1_05.txt, 1_06.txt, 1_07.txt, 1_08.txt, 1_09.txt, 1_10.txt, 1_11.txt, 1_12.txt, 1_13.txt, 1_14.txt, 1_15.txt, 1_16.txt, 1_17.txt, 1_18.txt, 1_19.txt, 1_20.txt, 1_21.txt, 1_22.txt, 1_23.txt, 1_24.txt, 1_25.txt, 1_26.txt, 1_27.txt, 1_28.txt |
Case Name |
Status |
Exec Time |
Memory |
0_00.txt |
AC |
20 ms |
27264 KB |
0_01.txt |
AC |
23 ms |
27264 KB |
0_02.txt |
AC |
23 ms |
27264 KB |
0_03.txt |
AC |
21 ms |
27264 KB |
1_00.txt |
AC |
22 ms |
27264 KB |
1_01.txt |
AC |
493 ms |
27392 KB |
1_02.txt |
AC |
1439 ms |
27392 KB |
1_03.txt |
AC |
20 ms |
27264 KB |
1_04.txt |
AC |
24 ms |
27392 KB |
1_05.txt |
AC |
27 ms |
27264 KB |
1_06.txt |
AC |
62 ms |
27392 KB |
1_07.txt |
AC |
33 ms |
27264 KB |
1_08.txt |
AC |
78 ms |
27392 KB |
1_09.txt |
AC |
114 ms |
27392 KB |
1_10.txt |
AC |
60 ms |
27264 KB |
1_11.txt |
AC |
230 ms |
27392 KB |
1_12.txt |
AC |
117 ms |
27392 KB |
1_13.txt |
AC |
601 ms |
27392 KB |
1_14.txt |
AC |
282 ms |
27392 KB |
1_15.txt |
AC |
392 ms |
27392 KB |
1_16.txt |
AC |
468 ms |
27392 KB |
1_17.txt |
AC |
24 ms |
27392 KB |
1_18.txt |
AC |
24 ms |
27264 KB |
1_19.txt |
AC |
23 ms |
27392 KB |
1_20.txt |
AC |
30 ms |
27392 KB |
1_21.txt |
AC |
22 ms |
27392 KB |
1_22.txt |
AC |
21 ms |
27392 KB |
1_23.txt |
AC |
21 ms |
27392 KB |
1_24.txt |
AC |
21 ms |
27392 KB |
1_25.txt |
AC |
21 ms |
27264 KB |
1_26.txt |
AC |
21 ms |
27392 KB |
1_27.txt |
AC |
21 ms |
27264 KB |
1_28.txt |
AC |
21 ms |
27392 KB |