Submission #668965

#	Time	Username	Problem	Language	Result	Execution time	Memory
668965		mychecksedad	The Xana coup (BOI21_xanadu)	C++17	100 / 100	80 ms	49588 KiB

xanadu

/* Author : Mychecksdead */
#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
#define pb push_back
#define all(x) x.begin(), x.end()
const int N = 1e6 + 5;

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

void dfs(int v, int p){
    vector<ll> no, yes;
    ll no_sum = 0, yes_sum = 0;
    for(int u: g[v]){
        if(u == p) continue;

        dfs(u, v);
    
        no_sum += dp[u][0][0];
        yes_sum += dp[u][0][1];
    
        no.pb(dp[u][1][0] - dp[u][0][0]);
        yes.pb(dp[u][1][1] - dp[u][0][1]);
    }

    sort(all(no));
    sort(all(yes));

    int s = no.size();

    dp[v][0][a[v]] = no_sum;
    dp[v][1][a[v]^1] = yes_sum + 1;


    for(int i = 0; i < s; ++i){
        bool state = (i + 1) % 2;
    
        no_sum += no[i];
        yes_sum += yes[i];

        dp[v][0][a[v] ^ state] = min(dp[v][0][a[v] ^ state], no_sum);
        dp[v][1][a[v] ^ state ^ 1] = min(dp[v][1][a[v] ^ state ^ 1], yes_sum + 1);
    }
}

void solve(){
    cin >> n;
    for(int i = 0; i < n - 1; ++i){
        int u, v; cin >> u >> v;
        g[u].pb(v);
        g[v].pb(u);
    }

    for(int i = 1; i <= n; ++i) cin >> a[i];

    for(int i = 1; i <= n; ++i) dp[i][0][0] = dp[i][0][1] = dp[i][1][0] = dp[i][1][1] = N;

    dfs(1, 0);

    if(min(dp[1][0][0], dp[1][1][0]) >= N){
        cout << "impossible";
    }else{
        cout << min(dp[1][0][0], dp[1][1][0]);
    }
}




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

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