Submission #1012019

#	Time	Username	Problem	Language	Result	Execution time	Memory
1012019		overwatch9	The Xana coup (BOI21_xanadu)	C++17	55 / 100	91 ms	20748 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
vector <vector <int>> adj;
const int maxn = 1e5 + 1;
int dp[maxn][2][2];
bool ready[maxn][2][2];
int state[maxn];
int solve(int s, int p, bool pressed_parent, bool pressed_now) {
    int cur_color = (state[s] + pressed_parent + pressed_now) % 2;
    int sz = adj[s].size();
    if (s != p)
        sz--;
    if (sz == 0 && s != p) {
        if (cur_color == 0)
            return 0;
        return 1e9;
    }
    if (ready[s][pressed_parent][pressed_now])
        return dp[s][pressed_parent][pressed_now];
    int best = 1e9;
    for (int i = 0; i < (1 << sz); i++) {
        int tp = 0;
        for (int j = 0, cnt = 0; cnt < sz; j++) {
            if (adj[s][j] == p)
                continue;
            bool y = i & (1 << cnt);
            tp += solve(adj[s][j], s, pressed_now, y);
            if (tp >= 1e9)
                break;
            cnt++;
        }
        tp += __builtin_popcount(i);
        if ((__builtin_popcount(i) + cur_color) % 2 == 0)
            best = min(best, tp);
    }
    ready[s][pressed_parent][pressed_now] = true;
    dp[s][pressed_parent][pressed_now] = best;
    return best;
}
int main() {
    int n;
    cin >> n;
    adj.resize(n+1);
    for (int i = 0; i < n-1; i++) {
        int a, b;
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    for (int i = 1; i <= n; i++)
        cin >> state[i];
    int res = solve(1, 1, 0, 0);
    int res2 = solve(1, 1, 0, 1) + 1;
    if (min(res, res2) == 1e9)
        cout << "impossible\n";
    else
        cout << min(res, res2) << '\n';
}

• Subtask 1: 5 / 5
• Subtask 2: 0 / 15
• Subtask 3: 10 / 10
• Subtask 4: 40 / 40
• Subtask 5: 0 / 30