Submission #546862

#	Time	Username	Problem	Language	Result	Execution time	Memory
546862		_martynas	The Xana coup (BOI21_xanadu)	C++11	100 / 100	62 ms	27568 KiB

xanadu

#include <bits/stdc++.h>

using namespace std;

using ll = long long;

const int MXN = 1e5+5;
const int INF = 1e6;

int n;
vector<int> Adj[MXN];
bool On[MXN];
// off/on, not clicked/clicked
ll dp[MXN][2][2];

void dfs(int u, int p)
{
    if(Adj[u].size() <= (p != -1)) {
        //cerr << u << " leaf\n";
        // leaf
        dp[u][On[u]][0] = 0;
        dp[u][!On[u]][1] = 1;
        return;
    }

    // all off/on, even clicked/odd clicked
    ll sub[2][2][2] = {};
    int fr = 1, to = 0;
    bool first = true;

    //cerr << u << ":\n";
    for(int v : Adj[u]) {
        if(v == p)
            continue;
        dfs(v, u);
        for(int i = 0; i < 4; i++) {
            sub[to][i&1][(i&2)>>1] = INF;
        }
        if(first) {
            for(int i = 0; i < 4; i++) {
                sub[to][i&1][(i&2)>>1] = dp[v][i&1][(i&2)>>1];
            }
            first = false;
            swap(fr, to);
            continue;
        }

//        cerr << "from:\n";
//        for(int i = 0; i < 4; i++) {
//            cerr << sub[fr][(i&2)>>1][i&1] << " ";
//        }
//        cerr << "\n";
        // off, not clicked
        sub[to][0][0] = min(sub[to][0][0], sub[fr][0][0] + dp[v][0][0]);
        sub[to][0][1] = min(sub[to][0][1], sub[fr][0][1] + dp[v][0][0]);
        // off, clicked
        sub[to][0][0] = min(sub[to][0][0], sub[fr][0][1] + dp[v][0][1]);
        sub[to][0][1] = min(sub[to][0][1], sub[fr][0][0] + dp[v][0][1]);
        // on, not clicked
        sub[to][1][0] = min(sub[to][1][0], sub[fr][1][0] + dp[v][1][0]);
        sub[to][1][1] = min(sub[to][1][1], sub[fr][1][1] + dp[v][1][0]);
        // on, clicked
        sub[to][1][0] = min(sub[to][1][0], sub[fr][1][1] + dp[v][1][1]);
        sub[to][1][1] = min(sub[to][1][1], sub[fr][1][0] + dp[v][1][1]);

//        cerr << "to:\n";
//        for(int i = 0; i < 4; i++) {
//            cerr << sub[to][(i&2)>>1][i&1] << " ";
//        }
//        cerr << "\n";

        swap(fr, to);
    }

    // all are off, don't click
    dp[u][On[u]][0] = sub[fr][0][0];
    dp[u][!On[u]][0] = sub[fr][0][1];
    // all are on, click
    dp[u][!On[u]][1] = 1+sub[fr][1][0];
    dp[u][On[u]][1] = 1+sub[fr][1][1];
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);

    cin >> n;

    for(int i = 0; i < n - 1; i++) {
        int a, b;
        cin >> a >> b;
        a--, b--;
        Adj[a].push_back(b);
        Adj[b].push_back(a);
    }

    for(int i = 0; i < n; i++) {
        cin >> On[i];
    }

    for(int i = 0; i < n; i++) {
        for(int j = 0; j < 4; j++) {
            dp[i][j&1][(j&2)>>1] = INF;
        }
    }

    dfs(0, -1);

//    for(int i = 0; i < n; i++) {
//        cerr << i << ":\n";
//        for(int j = 0; j < 4; j++) {
//            cerr << " " << dp[i][(j&2)>>1][j&1];
//        }
//        cerr << "\n";
//    }

    ll ans = min(dp[0][0][0], dp[0][0][1]);

    if(ans >= INF) {
        cout << "impossible\n";
    }
    else {
        cout << ans << "\n";
    }

    return 0;
}
/*
5
1 2
1 3
2 4
2 5
0 1 0 1 1

5
1 2
2 3
3 4
4 5
0 1 1 1 1

*/

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