Submission #847440

#	Time	Username	Problem	Language	Result	Execution time	Memory
847440		MinaRagy06	The Xana coup (BOI21_xanadu)	C++17	100 / 100	64 ms	28088 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
typedef int64_t ll;

const int N = 100'005;
int n, dp[N][2][2], a[N];
vector<int> adj[N];
int dfs(int i, int par, int parf, int curf) {
    if (~dp[i][parf][curf]) {
        return dp[i][parf][curf];
    }
    vector<int> newadj;
    for (auto nxt : adj[i]) {
        if (nxt == par) continue;
        newadj.push_back(nxt);
        dfs(nxt, i, curf, 0);
        dfs(nxt, i, curf, 1);
    }
    adj[i] = newadj;
    int m = adj[i].size();
    int dp2[m + 1][2]{};
    memset(dp2, '?', sizeof dp2);
    dp2[m][a[i] ^ parf ^ curf] = curf;
    for (int j = m - 1; j >= 0; j--) {
        for (int k = 0; k < 2; k++) {
            dp2[j][k] = min(dp2[j + 1][k ^ 1] + dp[adj[i][j]][curf][1], dp2[j + 1][k] + dp[adj[i][j]][curf][0]);
            dp2[j][k] = min(dp2[j][k], int(1e9));
        }
    }
    return dp[i][parf][curf] = dp2[0][0];
}
int main() {
    ios_base::sync_with_stdio(0), cin.tie(0);
    cin >> n;
    for (int i = 1, u, v; i < n; i++) {
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
    }
    memset(dp, -1, sizeof dp);
    int ans1 = dfs(1, 0, 0, 0);
    int ans2 = dfs(1, 0, 0, 1);
    if (min(ans1, ans2) >= int(1e9)) {
        cout << "impossible\n";
    } else {
        cout << min(ans1, ans2) << '\n';
    }
    return 0;
}

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