Submission #1151312

#	Time	Username	Problem	Language	Result	Execution time	Memory
1151312		vladilius	Star Trek (CEOI20_startrek)	C++20	43 / 100	1093 ms	327680 KiB

startrek

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define pb push_back
#define ff first
#define ss second
const int mod = 1e9 + 7;

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    
    int n; ll d; cin>>n>>d;
    vector<int> g[n + 1];
    for (int i = 1; i < n; i++){
        int u, v; cin>>u>>v;
        g[u].pb(v);
        g[v].pb(u);
    }
    
    vector<vector<int>> p(n + 1, vector<int>(n + 1)), h(n + 1, vector<int>(n + 1));
    function<void(int, int, int&)> fill = [&](int v, int pr, int& u){
        p[u][v] = pr; h[u][v] = 1;
        for (int i: g[v]){
            if (i == pr) continue;
            fill(i, v, u);
            h[u][v] = min(h[u][v], h[u][i]);
        }
        h[u][v] = !h[u][v];
    };
    
    for (int i = 1; i <= n; i++){
        fill(i, 0, i);
    }
    
    vector<vector<vector<bool>>> f(n + 1, vector<vector<bool>>(n + 1, vector<bool>(2)));
    function<void(int, int&)> dfs = [&](int v, int& u){
        int s = 0, x = 0;
        for (int i: g[v]){
            if (i == p[u][v]) continue;
            if (!h[u][i]){
                s++;
                x = i;
            }
        }
        for (int i: g[v]){
            if (i == p[u][v]) continue;
            f[u][i][0] = f[u][v][1];
            if (!s || (s == 1 && i == x)){
                f[u][i][1] = f[u][v][0];
            }
            else {
                f[u][i][1] = f[u][v][1];
            }
            dfs(i, u);
        }
    };
    
    for (int i = 1; i <= n; i++){
        f[i][i][0] = 0; f[i][i][1] = 1;
        dfs(i, i);
    }

    vector<vector<int>> dp(n + 1, vector<int>(2));
    vector<int> c1(n + 1), c0(n + 1);
    int S0 = 0, S1 = 0;
    for (int i = 1; i <= n; i++){
        dp[i][h[i][i]] = 1;
        for (int j = 1; j <= n; j++){
            if (f[i][j][1]){
                c1[i]++;
            }
            else {
                c0[i]++;
            }
        }
        S0 = (S0 + c0[i]) % mod;
        S1 = (S1 + c1[i]) % mod;
    }
    
    int h0 = 0, h1 = 0, s0 = 0, s1 = 0;
    for (int i = 1; i <= n; i++){
        if (h[i][i]) h1++;
        else h0++;
        
        s0 = (s0 + dp[i][0]) % mod;
        s1 = (s1 + dp[i][1]) % mod;
    }

    int out = dp[1][1];
    for (int i = 1; i <= d; i++){
        out = (1LL * c1[1] * s0) % mod;
        if (h[1][1]) out = (out + 1LL * s1 * n) % mod;
        int x = s0, y = s1;
        s0 = (1LL * x * S0 + 1LL * y * n * h0) % mod;
        s1 = (1LL * x * S1 + 1LL * y * n * h1) % mod;
    }
    cout<<out<<"\n";
}

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