Submission #487859

#	Time	Username	Problem	Language	Result	Execution time	Memory
487859		cfalas	The Xana coup (BOI21_xanadu)	C++14	10 / 100	106 ms	23772 KiB

xanadu

#include<bits/stdc++.h>
using namespace std;
#define mp make_pair
#define INF 10000000
#define MOD 1000000007
#define MID ((l+r)/2)
#define HASHMOD 2305843009213693951
#define ll long long
#define ull unsigned long long
#define F first
#define S second
typedef pair<ll, ll> ii;
typedef pair<ii, int> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef map<int, int> mii;

#define EPS 1e-6
#define FOR(i,n) for(int i=0;i<((int)(n));i++)
#define FORi(i,a,b) for(int i=((int)(a));i<((int)(b));i++)
#define FOA(v, a) for(auto v : a)

int t, n;
vi a, b;

vector<vi> adj;
ll dp[500000][2][2];
ll dfs(int s, int x, int xp, int p=0){
	if(dp[s][x][xp]!=-1) return dp[s][x][xp];
	ll ans=0;
	int c = a[s];
	if(xp) c = 1-c;
	if(x) c = 1-c, ans++;
	if((adj[s].size()==2 && p!=0) || (p==0 && adj[s].size()==1)){
		//cout<<s<<" "<<x<<" "<<xp<<" C 1\n";
		FOA(v, adj[s]){
			if(v!=p) ans+= dfs(v, c, x, s);
		}
	}
	else if((adj[s].size()==3 && p!=0) || (p==0 && adj[s].size()==2)){
		ll a1=0, a2=0;
		if(c==0){
			//cout<<s<<" "<<x<<" "<<xp<<" C 21\n";
			FOA(v, adj[s]){
				if(v!=p) a1+= dfs(v, 1, x, s);
				if(v!=p) a2+= dfs(v, 0, x, s);
			}
		}
		else{
			//cout<<s<<" "<<x<<" "<<xp<<" C 22\n";
			int cnt=0;
			FOA(v, adj[s]){
				if(v==p) continue;
				a1+= dfs(v, cnt, x, s);
				a2+= dfs(v, 1-cnt, x, s);
				cnt = 1-cnt;
			}
		}
		ans += min(a1, a2);

	}
	if(adj[s].size()==1 && c!=0) ans = MOD;
	dp[s][x][xp] = ans;
	//cout<<s<<" "<<x<<" "<<xp<<": "<<ans<<endl;
	return ans;
}

int main(){
	cin>>n;
	adj.assign(n+1, vi());
	FOR(i,n+2) dp[i][0][0] = dp[i][0][1] = dp[i][1][0] = dp[i][1][1] = -1;
	FOR(i,n-1){
		int a, b;
		cin>>a>>b;
		adj[a].push_back(b);
		adj[b].push_back(a);
	}
	a.resize(n+1);
	b.resize(n+1);
	FOR(i,n){
		cin>>a[i+1];
	}
	ll ans1 = dfs(1, 0, 0);
	ll ans2 = dfs(1, 1, 0);
	if(ans1 >= MOD && ans2 >= MOD) cout<<"impossible\n";
	else cout<<min(ans1, ans2);
}

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