Cf D. Nauuo and Circle

https://codeforces.com/contest/1173/problem/D

Meaning of the questions:

　　Gives you a tree contains n points, the n points numbered 1 ~ n;

　　Given a circle, a circle is placed on the n-th position, a position corresponding to the i-th node in the tree, and will not be repeated;

　　After seeking reduction tree in a circle such that the total number of non-intersecting edges embodiment;

Learning a: https: //www.cnblogs.com/violet-acmer/p/10991346.html

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int mod=998244353;
const int M=2e5+5;
struct node{
    int nextt,v;
}e[M<<1];
vector<int>son[M];
int head[M],n,tot;
ll fac[M],dp[M];
void addedge(int u,int v){
    e[tot].v=v;
    e[tot].nextt=head[u];
    head[u]=tot++;
}
void dfs(int u,int f){
    for(int i=head[u];~i;i=e[i].nextt){
        int v=e[i].v;
        if(v==f)
            continue;
        son[u].push_back(v);
        dfs(v,u);
    }
    int flag=0;
    if(u!=1)
        flag=1;
    int k=son[u].size()+flag;
    dp[u]=fac[k];
    for(int i=0;i<son[u].size();i++){
        dp[u]=dp[u]*dp[son[u][i]]%mod;
    }
}
ll solve(){
    dfs(1,1);
    return dp[1]*n%mod;
}
int main(){
    scanf("%d",&n);
    fac[0]=1;
    for(int i=1;i<=n;i++)
        fac[i]=(i*fac[i-1])%mod;
    memset(head,-1,sizeof(head));
    for(int i=1;i<n;i++){
        int u,v;
        scanf("%d%d",&u,&v);
        addedge(u,v);
        addedge(v,u);
    }
    printf("%I64d",solve());
    return 0;
}

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