Submission #1249480

#	Time	Username	Problem	Language	Result	Execution time	Memory
1249480		antonn	The Xana coup (BOI21_xanadu)	C++20	100 / 100	61 ms	24904 KiB

xanadu

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int N = 1e5 + 7;

int a[N], dp[N][2][2];
vector<int> g[N];

void dfs(int u, int p = 0) {
    vector<int> kids;
    for (auto v : g[u]) {
        if (v != p) {
            dfs(v, u);
            kids.push_back(v);
        }
    }
    if (kids.size() == 0) {
        dp[u][0][0] = 0;
        dp[u][1][1] = 1;
        return;
    }
    for (int val = 0; val < 2; ++val) {
        vector<int> mn(2, 1e9);
        if (val == 1) {
            mn[1] = 1;
        } else {
            mn[0] = 0;
        }
        for (auto v : kids) {
            vector<int> nwmn(2, 1e9);
            for (int i = 0; i < 2; ++i) {
                for (int t = 0; t < 2; ++t) {
                    for (int s = 0; s < 2; ++s)  {
                        if (s ^ val != a[v]) continue;
                        nwmn[i ^ t] = min(nwmn[i ^ t], mn[i] + dp[v][t][s]); 
                    }
                }
            }
            swap(nwmn, mn);
        }
        dp[u][val][0] = min(dp[u][val][0], mn[0]);
        dp[u][val][1] = min(dp[u][val][1], mn[1]);
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    for (int i = 1; i < n; ++i) {
        int a, b;
        cin >> a >> b;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    for (int i = 1; i <= n; ++i) {
        cin >> a[i];
    }
    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;
            }
        }
    }
    dfs(1);
    int ans = 1e9;
    for (int t = 0; t < 2; ++t) ans = min(ans, dp[1][t][a[1]]);
    if (ans == 1e9) {
        cout << "impossible\n";
        return 0;
    }
    cout << ans << "\n";
    return 0;
}
/*
5
2 1
3 2
4 2
5 2
0 1 1 0 1
*/

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