Submission #643965

#	Time	Username	Problem	Language	Result	Execution time	Memory
643965		alextodoran	The Xana coup (BOI21_xanadu)	C++17	100 / 100	74 ms	18180 KiB

xanadu

/**
 ____ ____ ____ ____ ____
||a |||t |||o |||d |||o ||
||__|||__|||__|||__|||__||
|/__\|/__\|/__\|/__\|/__\|

**/

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int N_MAX = 100000;
const int INF = INT_MAX / 2;

int N;
vector <int> adj[N_MAX + 2];
bool on[N_MAX + 2];

int dp[N_MAX + 2][2][2];

void dfs (int u, int parent = 0) {
    int sum[2][2];
    sum[0][0] = sum[0][1] = 0;
    sum[1][0] = sum[1][1] = INF;
    for (int v : adj[u]) {
        if (v != parent) {
            dfs(v, u);
            int old[2][2];
            old[0][0] = sum[0][0]; old[0][1] = sum[0][1];
            old[1][0] = sum[1][0]; old[1][1] = sum[1][1];
            sum[0][0] = min({old[0][0] + dp[v][0][0], old[1][0] + dp[v][1][0], INF});
            sum[0][1] = min({old[0][1] + dp[v][0][1], old[1][1] + dp[v][1][1], INF});
            sum[1][0] = min({old[0][0] + dp[v][1][0], old[1][0] + dp[v][0][0], INF});
            sum[1][1] = min({old[0][1] + dp[v][1][1], old[1][1] + dp[v][0][1], INF});
        }
    }
    if (on[u] == 1) {
        dp[u][0][0] = sum[1][0];
        dp[u][0][1] = sum[0][0];
        dp[u][1][0] = sum[0][1] + 1;
        dp[u][1][1] = sum[1][1] + 1;
    } else {
        dp[u][0][0] = sum[0][0];
        dp[u][0][1] = sum[1][0];
        dp[u][1][0] = sum[1][1] + 1;
        dp[u][1][1] = sum[0][1] + 1;
    }
}

int main () {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    cin >> N;
    for (int i = 1; i <= N - 1; i++) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    for (int u = 1; u <= N; u++) {
        cin >> on[u];
    }
    dfs(1);
    int answer = min(dp[1][0][0], dp[1][1][0]);
    if (answer <= N) {
        cout << answer << "\n";
    } else {
        cout << "impossible\n";
    }

    return 0;
}

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