Submission #1188811

#	Time	Username	Problem	Language	Result	Execution time	Memory
1188811		12345678	Star Trek (CEOI20_startrek)	C++20	0 / 100	2 ms	2632 KiB

startrek

#include <bits/stdc++.h>

using namespace std;

#define ll long long

const int nx=1e5+5, mod=1e9+7;

ll n, k, u, v, dp[nx], dpr[nx], lvl[nx], force[nx], lcnt, res;
vector<int> d[nx];

void dfs(int u, int p)
{
    lvl[u]=lvl[p]+1;
    for (auto v:d[u]) if (v!=p) dfs(v, u), dp[u]|=!dp[v];
}

void fillforce(int u, int p)
{
    int cnt=0;
    if (!dp[u])
    {
        for (auto v:d[u]) if (v!=p) cnt++;
        if (cnt==1) for (auto v:d[u]) if (v!=p) force[v]=1, fillforce(v, u);
    }
    else
    {
        for (auto v:d[u]) if (v!=p&&!dp[v]) cnt++;
        if (cnt==1) for (auto v:d[u]) if (v!=p&&!dp[v]) force[v]=1, fillforce(v, u);
    }
}

void dfs2(int u, int p)
{
    lcnt+=!(dp[u]|dpr[u]);
    //cout<<"debug "<<u<<' '<<dp[u]<<' '<<dpr[u]<<'\n';
    int cnt=0;
    for (auto v:d[u]) if (v!=p&&!dp[v]) cnt++;
    for (auto v:d[u])
    {
        if (v==p) continue;
        if (cnt-!dp[v]) dpr[v]=1;
        dfs2(v, u);
    }
}

int main()
{
    cin.tie(NULL)->sync_with_stdio(false);
    cin>>n>>k;
    for (int i=1; i<n; i++) cin>>u>>v, d[u].push_back(v), d[v].push_back(u);
    dfs(1, 1);
    force[1]=1;
    fillforce(1, 1);
    dfs2(1, 1);
    //cout<<"lcnt "<<lcnt<<'\n';
    for (int i=1; i<=n; i++)
    {
        if (lvl[i]%2)
        {
            if (dp[i]) res=(res+n)%mod;
            else 
            {
                if (force) res=(res+lcnt)%mod;
            }
        }
        else
        {
            if (!dp[i]) 
            {
                if (force) res=(res+(n-lcnt))%mod;
                else res=(res+n)%mod;
            }
        }
        //cout<<i<<' '<<res<<'\n';
    }
    cout<<res;
}

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