Submission #676750

#	Time	Username	Problem	Language	Result	Execution time	Memory
676750		Vahe	The Xana coup (BOI21_xanadu)	C++17	10 / 100	139 ms	26064 KiB

xanadu

#include <iostream>
#include <vector>
#include <set>
#include <queue>
#include <deque>
#include <map>
#include <stack>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <climits>
using namespace std;
using ll = long long;
int n;
vector<int> clr;
vector<vector<int>> gp;
vector<vector<vector<int>>> dp;

void DPcreator(int u, int p, int nerk)
{
    multiset<pair<int, int>> st;

    for (int& v : gp[u])
    {
        if (v == p) continue;
        if (dp[v][0][nerk] < 2e9) st.insert({ dp[v][0][nerk], 0 });
        if (dp[v][1][nerk] < 2e9) st.insert({ dp[v][1][nerk], 1 });
    }
    int sum = 0, cnt = clr[u] + nerk, q = gp[u].size() - (p != -1);
    int f0 = -1, f1 = -1, s0 = -1, s1 = -1;
    for (pair<int, int> i : st)
    {
        if (q)
        {
            q--;
            cnt += i.second;
            sum += i.first;
            i.second ? (f1 = i.first) : (f0 = i.first);
        }
        else
        {
            if (i.second && s1 == -1) s1 = i.first;
            if (!i.second && s0 == -1) s0 = i.first;
        }
    }
    int NotChanged = sum + nerk;

    // Changing...
    if ((f0 == -1 || s1 == -1) && (f1 == -1 || s0 == -1)) sum = 2e9;
    else if (f0 != -1 && s1 != -1 && f1 != -1 && s0 != -1) sum += min(s1 - f0, s0 - f1);
    else if (f0 == -1 || s1 == -1) sum += s0 - f1;
    else sum += s1 - f0;

    int Changed = sum + nerk;
    //
    if (q) NotChanged = Changed = 2e9;
    //
    if (cnt & 1) dp[u][nerk][0] = Changed, dp[u][nerk][1] = NotChanged;
    else         dp[u][nerk][0] = NotChanged, dp[u][nerk][1] = Changed;
}

void dfs(int u, int p)
{
    if (gp[u].size() == 1 && u != 0)
    {
        if (clr[u])
        {
            dp[u][0][0] = 2e9;
            dp[u][0][1] = 0;
            dp[u][1][0] = 1;
            dp[u][1][1] = 2e9;
        }
        else
        {
            dp[u][0][0] = 0;
            dp[u][0][1] = 2e9;
            dp[u][1][0] = 2e9;
            dp[u][1][1] = 1;
        }
        return;
    }

    for (int& v : gp[u])
    {
        if (v == p) continue;
        if (dp[v][0][0] == -1) dfs(v, u);
    }
    
    DPcreator(u, p, 0);
    DPcreator(u, p, 1);
}

int main() {
    int n; cin >> n;
    gp = vector<vector<int>>(n);
    dp = vector<vector<vector<int>>>(n, { {-1, -1}, {-1, -1} });

    for (int i = 1; i < n; i++)
    {
        int u, v; cin >> u >> v;
        gp[--u].push_back(--v);
        gp[v].push_back(u);
    }
    clr = vector<int>(n);
    for (int& i : clr) cin >> i;

    dfs(0, -1);

    int ans = min(dp[0][0][0], dp[0][1][0]);
    if (ans >= 2e9) puts("impossible");
    else printf("%d\n", ans);
    return 0;
}

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