Submission #5543200

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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);
vector<P> dp2(1001);
int n;
 
P dfs(int u,int prev){
    dp[u] = 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);
        dp[u].sc += p.sc;
        dp[u].fs = dp[u].fs*combi(dp[u].sc,p.sc)%mod*p.fs%mod;
    }
    dp[u].sc++;
    return dp1[u];
}


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,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

Compile Error

./Main.cpp: In function ‘P dfs(int, int)’:
./Main.cpp:61:5: error: ‘dp’ was not declared in this scope
     dp[u] = mp(1,0);
     ^