Submission #482136

#	Time	Username	Problem	Language	Result	Execution time	Memory
482136		PoPularPlusPlus	The Xana coup (BOI21_xanadu)	C++17	100 / 100	96 ms	18444 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long 
#define pb(e) push_back(e)
#define sv(a) sort(a.begin(),a.end())
#define sa(a,n) sort(a,a+n)
#define mp(a,b) make_pair(a,b)
#define vf first
#define vs second
#define ar array
#define all(x) x.begin(),x.end()
const int inf = 0x3f3f3f3f;
const int mod = 1000000007; 
const double PI=3.14159265358979323846264338327950288419716939937510582097494459230;
bool remender(ll a , ll b){return a%b;}

const int N = 100003;
vector<int> adj[N];
int dp[N][2][2];
int arr[N];

void dfs(int node , int par = -1){
	dp[node][0][0] = dp[node][1][0] = 0;
	dp[node][0][1] = dp[node][1][1] = 1;
	for(int i : adj[node]){
		if(i != par)dfs(i,node);
	}
	for(int t1 = 0; t1 < 2; t1++){
		for(int t2 = 0; t2 < 2; t2++){
			int od = 1 - ((t2 + t1) % 2);
			int dif = N , dif1 = N , both = 0;
			int ans = 0 , cnt = 0;
			for(int i : adj[node]){
				if(i!=par){
					if(dp[i][(arr[i-1] + t2) % 2][0] == dp[i][(arr[i-1] + t2) % 2][1])both++;
					else if(dp[i][(arr[i-1] + t2) % 2][0] > dp[i][(arr[i-1] + t2) % 2][1]){
						dif = min(dif , dp[i][(arr[i-1] + t2) % 2][0] - dp[i][(arr[i-1] + t2) % 2][1]);
						cnt++;
						cnt %= 2;
					}
					else {
						dif1 = min(dif1 , dp[i][(arr[i-1] + t2) % 2][1] - dp[i][(arr[i-1] + t2) % 2][0]);
					}
					ans += min(dp[i][(arr[i-1] + t2) % 2][0] , dp[i][(arr[i-1]+t2)%2][1]);
					ans = min(ans , N);
				}
			}
			if(cnt == od && both == 0){
				ans += min(dif,dif1);
			}
			ans = min(ans , N);
			dp[node][t1][t2] += ans;
		}
	}
}

void solve(){
	int n;
	cin >> n;
	for(int i = 0; i < n-1; i++){
		int a , b;
		cin >> a >> b;
		adj[a].pb(b);
		adj[b].pb(a);
	}
	for(int i = 0; i < n; i++)cin >> arr[i];
	dfs(1);
	int res = min(dp[1][arr[0]][0] , dp[1][arr[0]][1]);
	if(res > n){
		cout << "impossible\n";
	}
	else cout << res << '\n';
}

int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
	//int t;cin >> t;while(t--)
	solve();
	return 0;
}

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