Submission #871583

#	Time	Username	Problem	Language	Result	Execution time	Memory
871583		Trisanu_Das	Star Trek (CEOI20_startrek)	C++17	45 / 100	45 ms	19664 KiB

startrek

#include<bits/stdc++.h>
 
using namespace std;
 
typedef long long ll;
typedef long double ld;
 
const int N=1e5+5;
const ll mod=1e9+7;
 
ll binpow(ll a,ll b){
    ll res=1;
    while(b>0){
        if(b&1)res*=a,res%=mod;
        a*=a,a%=mod;
        b>>=1;
    }
    return res;
}
 
int n;
ll d,ans,sum;
vector<int> adj[N];
ll dp[N][4];
bool dp1[N],dp2[N];
 
void dfs(int u,int p){
    for(auto v:adj[u]){
        if(v==p)continue;
        dfs(v,u);
        dp1[u]|=!dp1[v];
    }
}
 
void dfs2(int u,int p,bool w){
    int cnt=!w;
    dp2[u]=dp1[u]|!w;
    for(auto v:adj[u]){
        if(v==p)continue;
        cnt+=!dp1[v];
    }
    for(auto v:adj[u]){
        if(v==p)continue;
        dfs2(v,u,cnt-!dp1[v]>0);
    }
}
 
void dfs3(int u,int p){
    int cnt=0;
    for(auto v:adj[u]){
        if(v==p)continue;
        cnt+=!dp1[v];
    }
    for(auto v:adj[u]){
        if(v==p)continue;
        dfs3(v,u);
        dp[u][0]+=dp[v][1];
        if(cnt-!dp1[v]>0)dp[u][0]+=dp[v][0];
        else dp[u][1]+=dp[v][0];
        dp[u][0]%=mod;
        dp[u][1]%=mod;
    }
    dp[u][0]+=n-sum;
    if(dp1[u])dp[u][0]+=sum;
    else dp[u][1]+=sum;
    dp[u][0]%=mod;
    dp[u][1]%=mod;
}
 
int main(){
    cin.tie(nullptr)->sync_with_stdio(false);
    cin >> n >> d;
    if(n==2)cout << binpow(4,d),exit(0);
    for(int i=1;i<n;i++){
        int u,v;
        cin >> u >> v;
        adj[u].emplace_back(v);
        adj[v].emplace_back(u);
    }
    dfs(1,1);
    dfs2(1,1,true);
    for(int i=1;i<=n;i++)sum+=dp2[i];
    dfs3(1,1);
    cout << dp[1][0];
}

• Subtask 1: 0 / 0
• Subtask 2: 7 / 7
• Subtask 3: 8 / 8
• Subtask 4: 15 / 15
• Subtask 5: 15 / 15
• Subtask 6: 0 / 20
• Subtask 7: 0 / 20
• Subtask 8: 0 / 15