Submission #1017722

#	Time	Username	Problem	Language	Result	Execution time	Memory
1017722		vjudge1	The Xana coup (BOI21_xanadu)	C++17	100 / 100	50 ms	33092 KiB

xanadu

#include <bits/stdc++.h>

using namespace std;
using ll = long long;

#define int long long
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define FORD(i, a, b) for (int i = (b); i >= (a); i --)
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPD(i, n) for (int i = (n) - 1; i >= 0; --i)

#define MASK(i) (1LL << (i))
#define BIT(x, i) (((x) >> (i)) & 1)


constexpr ll LINF = (1ll << 60);
constexpr int INF = (1ll << 30);
constexpr int Mod = 1e9 + 7;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

/*
    Phu Trong from Nguyen Tat Thanh High School for gifted student
*/

template <class X, class Y>
    bool minimize(X &x, const Y &y){
        X eps = 1e-9;
        if (x > y + eps) {x = y; return 1;}
        return 0;
    }

template <class X, class Y>
    bool maximize(X &x, const Y &y){
        X eps = 1e-9;
        if (x + eps < y) {x = y; return 1;}
        return 0;
    }
#define MAX         200005
int numNode;
vector<int> G[MAX];
int label[MAX];
/*
    1. It is optimal to press a button at most once
    2. The pressing order is not important
*/

int dp[MAX][2][2];

void dfs(int u, int p = -1){
    vector<int> store[2];
    int sm_on = 0, sm_off = 0;
    for (int&v : G[u]) if(v ^ p){
        dfs(v, u);
        store[0].push_back(dp[v][0][1] - dp[v][0][0]);
        store[1].push_back(dp[v][1][1] - dp[v][1][0]);
        sm_off  += dp[v][0][0];
        sm_on   += dp[v][1][0];
    }

    REP(i, 2) sort(store[i].begin(), store[i].end());

    int min_odd = numNode + 1, min_even = 0, sm = 0;
    for (int i = 0; i < (int)store[0].size(); ++i){
        sm += store[0][i];
        if ((i + 1) & 1) minimize(min_odd, sm);
        else minimize(min_even, sm);
    }

    minimize(dp[u][label[u]][0], min_even + sm_off);
    minimize(dp[u][label[u] ^ 1][0], min_odd + sm_off);

    min_odd = numNode + 1, min_even = 0, sm = 0;
    for (int i = 0; i < (int)store[1].size(); ++i){
        sm += store[1][i];
        if ((i + 1) & 1) minimize(min_odd, sm);
        else minimize(min_even, sm);
    }

    minimize(dp[u][label[u]][1], min_odd + sm_on + 1);
    minimize(dp[u][label[u] ^ 1][1], min_even + sm_on + 1);
}
void process(void){
    cin >> numNode;
    for (int i = 1; i < numNode; ++i){
        int u, v; cin >> u >> v;
        G[u].emplace_back(v);
        G[v].emplace_back(u);
    }
    for (int i = 1; i <= numNode; ++i) cin >> label[i];
    for (int i = 1; i <= numNode; ++i) {
        REP(on, 2) REP(press, 2) dp[i][on][press] = numNode + 1;
    }
    dfs(1);
    int ans = min(dp[1][0][0], dp[1][0][1]);
    if(ans > numNode) return void(cout << "impossible");

    cout << ans;
}
signed main(){
    #define name "Whisper"
    cin.tie(nullptr) -> sync_with_stdio(false);
    //freopen(name".inp", "r", stdin);
    //freopen(name".out", "w", stdout);

    process();
}

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