Submission #919915

#	Time	Username	Problem	Language	Result	Execution time	Memory
919915		CyberCow	Star Trek (CEOI20_startrek)	C++17	45 / 100	70 ms	25668 KiB

startrek

#include <random>
#include <algorithm>
#include <bitset>
#include <chrono>
#include <cmath>
#include <deque>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
#include <chrono>
#define m_p make_pair
#define all(x) (x).begin(),(x).end()
#define sz(x) ((x).size())
typedef long long ll;
using namespace std;
mt19937 rnd(348502);
const ll N = 100010;
ll mod = 1e9 + 7;

ll binpow(ll a, ll x)
{
    if (x == 0)
        return 1;
    if (x % 2)
        return (a * binpow(a, x - 1)) % mod;
    return binpow((a * a) % mod, x / 2);
}

vector<ll> v[N];
ll dp[N][2];
ll dpv[N][2];

void Dfs(ll g, ll p)
{
    ll qan = 0, qan1 = 0, sz = 0;
    for (auto to : v[g])
    {
        if (to != p)
        {
            sz++;
            Dfs(to, g);
            if (dp[to][0])
                qan++;
            if (dp[to][1] == 1)
                qan1++;
        }
    }
    if (qan != sz)
    {
        dp[g][1] = 1;
    }
    if (qan1 != sz)
    {
        dp[g][0] = 1;
    }
}

void Dfs1(ll g, ll p, ll a, ll b)
{
    ll qan = a, qan1 = b, sz = v[g].size();
    for (auto to : v[g])
    {
        if (to != p)
        {
            qan += dp[to][0];
            qan1 += dp[to][1];
        }
    }
    if (qan != sz)
    {
        dpv[g][1] = 1;
    }
    if (qan1 != sz)
    {
        dpv[g][0] = 1;
    }
    for (auto to : v[g])
    {
        if(to != p)
        Dfs1(to, g, (qan1 - dp[to][1] != sz - 1), (qan - dp[to][0] != sz - 1));
    }
}

ll q0q0 = 0, q0q1 = 0, q1q0 = 0, q1q1 = 0;

ll dpans[N][2][2][2];

void Dfs2(ll g, ll p)
{
    ll qan = 0, qan1 = 0, sz = 0;
    for (auto to : v[g])
    {
        if (to != p)
        {
            sz++;
            Dfs2(to, g);
            if (dpans[to][0][0][1] == 1)
                qan++;
            if (dpans[to][0][1][1] == 1)
                qan1++;
        }
    }
    if (qan != sz)
    {
        dpans[g][0][1][1] = 1;
        dpans[g][1][1][1] += q1q0;
        dpans[g][1][1][1] += q1q1;
    }
    else
    {
        dpans[g][0][1][0] = 1;
        dpans[g][1][1][0] += q1q0;
        dpans[g][1][1][0] += q1q1;
    }
    if (qan1 != sz)
    {
        dpans[g][0][0][1] = 1;
        dpans[g][1][0][1] += q0q1;
        dpans[g][1][0][1] += q1q1;
    }
    else
    {
        dpans[g][0][0][0] = 1;
        dpans[g][1][0][0] += q0q1;
        dpans[g][1][0][0] += q1q1;
    }
    dpans[g][1][0][1] += q0q0;
    dpans[g][1][1][1] += q0q0;
    dpans[g][1][0][1] += q1q0;
    dpans[g][1][1][1] += q0q1;
    for (auto to : v[g])
    {
        if (to != p)
        {
            ll kop = qan;
            ll kop1 = qan1;
            kop -= dpans[to][0][0][1];
            kop1 -= dpans[to][0][1][1];
            if (kop != sz - 1)
            {
                dpans[g][1][1][1] += dpans[to][1][0][1];
                dpans[g][1][1][1] += dpans[to][1][0][0];
            }
            else
            {
                dpans[g][1][1][0] += dpans[to][1][0][1];
                dpans[g][1][1][1] += dpans[to][1][0][0];
            }
            if (kop1 != sz - 1)
            {
                dpans[g][1][0][1] += dpans[to][1][1][1];
                dpans[g][1][0][1] += dpans[to][1][1][0];
            }
            else
            {
                dpans[g][1][0][0] += dpans[to][1][1][1];
                dpans[g][1][0][1] += dpans[to][1][1][0];
            }
            dpans[g][1][1][1] %= mod;
            dpans[g][1][1][0] %= mod;
            dpans[g][1][0][1] %= mod;
            dpans[g][1][0][0] %= mod;
            dpans[g][0][1][1] %= mod;
            dpans[g][0][1][0] %= mod;
            dpans[g][0][0][1] %= mod;
            dpans[g][0][0][0] %= mod;
        }
    }
}

void solve()
{
    ll n, d, x, y;
    cin >> n >> d;
    if (n == 2)
    {
        for (ll i = 0; i < n - 1; i++)
        {
            cin >> x >> y;
        }
        cout << binpow(4, d);
    }
    else
    {
        for (ll i = 0; i < n - 1; i++)
        {
            cin >> x >> y;
            v[x].push_back(y);
            v[y].push_back(x);
        }
        Dfs(1, -1);
        Dfs1(1, -1, 0, 0);
        for (ll i = 1; i <= n; i++)
        {
            if (dpv[i][0] == 1 && dpv[i][1] == 1)
            {
                q1q1++;
            }
            if (dpv[i][0] == 0 && dpv[i][1] == 1)
            {
                q0q1++;
            }
            if (dpv[i][0] == 1 && dpv[i][1] == 0)
            {
                q1q0++;
            }
            if (dpv[i][0] == 0 && dpv[i][1] == 0)
            {
                q0q0++;
            }
        }
        Dfs2(1, -1);
        cout << dpans[1][1][1][1] % mod;
    }
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    ll tt = 1;
    //cout << (mod + -10000010 % mod) % mod;
    //cin >> tt;
    while (tt--) {
        solve();
    }
    return 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