Submission #783526

#	Time	Username	Problem	Language	Result	Execution time	Memory
783526		andecaandeci	The Xana coup (BOI21_xanadu)	C++17	100 / 100	52 ms	16624 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
#define fi first
#define se second

vector<int> adj[100005], depth2[100005];
queue<int> q;
int a[100005], depth1[100005];
bool vis[100005];
ll dp[100005][2][2];

int main() { 
    ios_base::sync_with_stdio(false); cin.tie(NULL);
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        for (int j = 0; j < 2; j++) {
            for (int k = 0; k < 2; k++) dp[i][j][k] = 1e9;
        }
    }
    for (int i = 0; i < n - 1; i++) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    for (int i = 1; i <= n; i++) cin >> a[i];
    q.push(1);
    vis[1] = 1;
    while (!q.empty()) {
        int x = q.front();
        q.pop();
        for (auto u : adj[x]) {
            if (vis[u]) continue;
            vis[u] = 1;
            depth1[u] = depth1[x] + 1;
            q.push(u);
        }
    }
    for (int i = 1; i <= n; i++) {
        vis[i] = 0;
        depth2[depth1[i]].push_back(i);
        if ((i != 1) and ((int)adj[i].size() == 1)) dp[i][0][a[i]] = 0, dp[i][1][1 - a[i]] = 1, vis[i] = 1;
    }
    for (int i = n - 1; i >= 0; i--) {
        for (auto x : depth2[i]) {
            if ((x != 1) and ((int)adj[x].size() == 1)) continue;
            dp[x][0][a[x]] = 0, dp[x][1][1 - a[x]] = 1, dp[x][0][1 - a[x]] = 1e9, dp[x][1][a[x]] = 1e9;
            for (auto u : adj[x]) {
                if (!vis[u]) continue;
                ll c1 = dp[x][0][0], c2 = dp[x][0][1], c3 = dp[x][1][0], c4 = dp[x][1][1];
                dp[x][0][0] = min(c1 + dp[u][0][0], c2 + dp[u][1][0]);
                dp[x][0][1] = min(c2 + dp[u][0][0], c1 + dp[u][1][0]);
                dp[x][1][0] = min(c3 + dp[u][0][1], c4 + dp[u][1][1]);
                dp[x][1][1] = min(c4 + dp[u][0][1], c3 + dp[u][1][1]);
            }
            vis[x] = 1;
        }
    }
    ll ans = min(dp[1][0][0], dp[1][1][0]);
    if (ans > n) cout << "impossible\n";
    else cout << ans << "\n";
}

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