Submission #678365

#	Time	Username	Problem	Language	Result	Execution time	Memory
678365		Vahe	The Xana coup (BOI21_xanadu)	C++17	100 / 100	180 ms	27648 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, zibil;

    bool impossible = 0;
    int MinChange = 2e9;
    for (int& v : gp[u])
    {
        if (v == p) continue;
        if (dp[v][0][nerk] < 2e9 && dp[v][1][nerk] < 2e9)
        {
            st.insert({ min(dp[v][0][nerk], dp[v][1][nerk]), (dp[v][0][nerk] < dp[v][1][nerk] ? 0 : 1) });
            MinChange = min(MinChange, abs(dp[v][0][nerk] - dp[v][1][nerk]));
        }
        else if (dp[v][0][nerk] < 2e9)
            st.insert({ dp[v][0][nerk], 0 });
        else if (dp[v][1][nerk] < 2e9)
            st.insert({ dp[v][1][nerk], 1 });
        else impossible = 1;
    }

    int sum = 0, cnt = clr[u] + nerk;
    for (pair<int, int> i : st)
    {
        cnt += i.second;
        sum += i.first;
    }

    int NotChanged = sum + nerk;

    sum += MinChange;

    int Changed = sum + nerk;
    //
    if (impossible) 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) cout << "impossible\n";
    else cout << ans << endl;

    //for (int i = 0; i < n; i++) { for (int j = 0; j < 2; j++) for (int k = 0; k < 2; k++) printf("dp[%d][%d][%d] = %d\n", i + 1, j, k, dp[i][j][k]); puts(""); }
    return 0;
}

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