Submission #677167

#	Time	Username	Problem	Language	Result	Execution time	Memory
677167		amir	The Xana coup (BOI21_xanadu)	C++14	100 / 100	84 ms	15512 KiB

xanadu

#include <bits/stdc++.h>

using namespace std;

typedef long long ll ;
typedef pair<int , int> pii ;
typedef pair<ll , ll> pll ;
#define ps push_back
#define pb pop_back
#define mp make_pair
#define all(x) x.begin() , x.end() 
#define sz(x) (int)x.size() 
#define debug(a) cout<<"debug: "<<(#a)<<" = "<<a<<'\n'
const ll maxn = 1e5 + 6 , inf = 1e10 +10 ;
ll dp[maxn][5] ;
ll col[maxn] ;
ll n ;
vector<ll > adj[maxn] ;

void dfs(ll v , ll p = -1){
	if (sz(adj[v]) == 1 && v != 1){
		if (col[v]){
			dp[v][2] = 0 ;
			dp[v][1] = 1 ;
		}
		else {
			dp[v][0] = 0 ;
			dp[v][3] = 1 ;
		}
		return ;
	}
	
	for (ll u : adj[v]){
		if (u != p){
			dfs(u ,v) ;
		}
	}
	ll mne = inf , sum = 0 ;
	ll cnt1 = 0 ;
	for (ll u : adj[v]){
		if (u == p) continue ;
		if (dp[u][1] <= dp[u][0]){
			cnt1 ++ ;
			sum += dp[u][1] ;
			mne = min(mne , (dp[u][0] - dp[u][1])) ;
		}
		else{
			sum += dp[u][0] ;
			mne = min(mne , (dp[u][1] - dp[u][0])) ;
		}
	}
	/*debug(v) ;
	debug(sum) ;
	debug(cnt1) ;
	debug(mne) ;
	cout << '\n' ;*/
	if (col[v]){
		if (cnt1 % 2){
			dp[v][0] = sum ;
			dp[v][2] = sum + mne ;
		}
		else {
			dp[v][2] = sum ;
			dp[v][0] = sum + mne ;
		}
	}
	else {
		if (cnt1 % 2){
			dp[v][2] = sum ;
			dp[v][0] = sum + mne ;
		}
		else {
			dp[v][0] = sum ;
			dp[v][2] = sum + mne ;
		}
	}
	
	mne = inf , sum = 0 ;
	cnt1 = 0 ;
	for (ll u : adj[v]){
		if (u == p) continue ;
		if (dp[u][3] <= dp[u][2]){
			cnt1 ++ ;
			sum += dp[u][3] ;
			mne = min(mne , (dp[u][2] - dp[u][3])) ;
		}
		else{
			sum += dp[u][2] ;
			mne = min(mne , (dp[u][3] - dp[u][2])) ;
		}
	}
	
	if (col[v]){
		if (cnt1 % 2){
			dp[v][3] = sum +1;
			dp[v][1] = sum + mne +1;
		}
		else {
			dp[v][1] = sum +1;
			dp[v][3] = sum + mne +1;
		}
	}
	else {
		if (cnt1 % 2){
			dp[v][1] = sum +1;
			dp[v][3] = sum + mne +1;
		}
		else {
			dp[v][3] = sum +1;
			dp[v][1] = sum + mne +1;
		}
	}
	return ;
}


int main()
{
    ios::sync_with_stdio(false) ; 
	cin.tie(NULL) ;
	cout.tie(NULL) ;
	cin >> n ;
	for (int i = 1 ; i <= n-1 ; i++){
		ll a , b ;
		cin >> a >> b ;
		adj[a].ps(b) ;
		adj[b].ps(a) ;
	}
	for (int i = 1 ;i <= n ; i++){
		cin >> col[i] ;
	}
	for (int i = 1 ; i <= n ; i++){
		for (int j = 0 ; j < 4 ; j++)
			dp[i][j] = inf ;
	}
	dfs(1) ;
	ll ans = min(dp[1][0] , dp[1][1]) ;
	if (ans > n){
		cout << "impossible\n" ;
		return 0 ;
	} 
	cout << ans << '\n' ;
}

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