Submission #791488

#	Time	Username	Problem	Language	Result	Execution time	Memory
791488		ttamx	Star Trek (CEOI20_startrek)	C++14	30 / 100	32 ms	468 KiB

startrek

#include<bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;

const int N=1005;
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][2];

bool dfs(int u,int p){
    bool res=true;
    for(auto v:adj[u]){
        if(v==p)continue;
        res&=dfs(v,u);
    }
    res^=true;
    return res;
}

bool dfs2(int u,int p,int t,bool w){
    bool res=true;
    for(auto v:adj[u]){
        if(v==p)continue;
        res&=dfs2(v,u,t,w);
    }
    if(u==t)res&=w;
    res^=true;
    return res;
}
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);
    }
    for(int i=1;i<=n;i++)sum+=dfs(i,i);
    for(int i=1;i<=n;i++)ans+=sum*dfs2(1,1,i,true)+(n-sum)*dfs2(1,1,i,false);
    cout << ans;
}

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