Submission #545188

#	Time	Username	Problem	Language	Result	Execution time	Memory
545188		Zhora_004	The Xana coup (BOI21_xanadu)	C++17	30 / 100	771 ms	66016 KiB

xanadu

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <unordered_set>
#include <queue>
#include <deque>
#include <string>
#include <sstream>
#include <iomanip>
#include <map>
#include <unordered_map>
#include <stack>
#include <cstdio>
#include <climits>
#include <tuple>
#include <ctime>
#include <cstring>
#include <numeric>
#include <functional>
#include <chrono>
#include <cassert>
#include <bitset>
//#include <bit>
//#include <ranges>
//#include <numbers>
#define itn int
#define sacnf scanf
#define sz(a) ((int)((a).size()))
// printf("%.10f\n", ans);
using ll = long long;
using namespace std;
const ll mod = 1e9 + 7;
const int N = 1e5 + 1, inf = 1e9;
int n;
vector<int> on;
vector<vector<int>> tree;

bool tc1()
{
    return n <= 20;
}

bool tc2()
{
    return n <= 40;
}

ll convert(vector<int>& v)
{
    ll res = 0, p = 1;
    for (int i = sz(v) - 1; i >= 0; i--)
    {
        if (v[i]) res += p;
        p <<= 1;
    }
    return res;
}

bool tc3()
{
    for (int a = 0; a < n; a++) for (int& b : tree[a]) if (abs(a - b) != 1) return 0;
    return 1;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cin >> n;
    on = vector<int>(n);
    tree = vector<vector<int>>(n);
    for (int i = 1; i < n; i++)
    {
        int u, v;
        cin >> u >> v;
        tree[--u].push_back(--v);
        tree[v].push_back(u);
    }
    for (int i = 0; i < n; i++) cin >> on[i];
    /*if (tc1())
    {
        int ans = 1e9;
        for (int mask = 0; mask < (1 << n); mask++)
        {
            vector<int> tmp = on;
            int cnt = 0;
            for (int i = 0; i < n; i++)
            {
                if ((mask >> i) & 1)
                {
                    int u = n - i - 1;
                    tmp[u] ^= 1;
                    for (int& v : tree[u]) tmp[v] ^= 1;
                    cnt++;
                }
            }
            bool flag = 1;
            for (int i = 0; i < n; i++)
            {
                if (tmp[i])
                {
                    flag = 0;
                    break;
                }
            }
            if (flag) ans = min(ans, cnt);
        }
        if (ans == 1e9) cout << "impossible";
        else cout << ans;
    }*/
    if (tc2())
    {
        int ans = 1e9;
        int k = (n - 1) / 2;
        int cnt = k + 1;
        map<ll, int> mp;
        ll req = convert(on);
        for (int mask = 0; mask < (1 << cnt); mask++)
        {
            vector<int> tmp = vector<int>(n);
            int ones = 0;
            for (int i = 0; i < cnt; i++)
            {
                if ((mask >> i) & 1)
                {
                    int u = cnt - i - 1;
                    tmp[u] ^= 1;
                    for (int& v : tree[u]) tmp[v] ^= 1;
                    ones++;
                }
            }
            ll num = convert(tmp);
            if (mp.find(num) == mp.end()) mp[num] = ones;
            else mp[num] = min(mp[num], ones);
        }
        cnt = n - 1 - (k + 1) + 1;
        for (int mask = 0; mask < (1 << cnt); mask++)
        {
            vector<int> tmp = vector<int>(n);
            int ones = 0;
            for (int i = 0; i < cnt; i++)
            {
                if ((mask >> i) & 1)
                {
                    int u = n - i - 1;
                    tmp[u] ^= 1;
                    for (int& v : tree[u]) tmp[v] ^= 1;
                    ones++;
                }
            }
            ll num = convert(tmp);
            if (mp.find(req ^ num) != mp.end()) ans = min(ans, mp[req ^ num] + ones);
        }
        if (ans == 1e9) cout << "impossible";
        else cout << ans;
        return 0;
    }
    if (tc3())
    {
        vector<vector<vector<int>>> dp(n, vector<vector<int>>(2, vector<int>(2)));
        if (on[0])
        {
            dp[0][0][0] = inf;
            dp[0][0][1] = 1;
            dp[0][1][0] = 0;
            dp[0][1][1] = inf;
        }
        else
        {
            dp[0][0][0] = 0;
            dp[0][0][1] = inf;
            dp[0][1][0] = inf;
            dp[0][1][1] = 1;
        }
        for (int i = 1; i < n; i++)
        {
            if (on[i])
            {
                dp[i][0][0] = dp[i - 1][0][1];
                dp[i][0][1] = dp[i - 1][1][0] + 1;
                dp[i][1][0] = dp[i - 1][0][0];
                dp[i][1][1] = dp[i - 1][1][1] + 1;
            }
            else
            {
                dp[i][0][0] = dp[i - 1][0][0];
                dp[i][0][1] = dp[i - 1][1][1] + 1;
                dp[i][1][0] = dp[i - 1][0][1];
                dp[i][1][1] = dp[i - 1][1][0] + 1;
            }
        }
        int ans = min(dp[n - 1][0][0], dp[n - 1][0][1]);
        if (ans > n) cout << "impossible";
        else cout << ans;
    }

    return 0;
}

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 0 / 40
• Subtask 5: 0 / 30