Submission #1128509

#	Time	Username	Problem	Language	Result	Execution time	Memory
1128509		Alihan_8	The Xana coup (BOI21_xanadu)	C++20	100 / 100	112 ms	39032 KiB

xanadu

#include <bits/stdc++.h>

using namespace std;

using i64 = long long;

void chmin(int &x, const int &y){
	x = min(x, y);
}

int dp[100005][2][2];

signed main(){
	int n; cin >> n;
	
	vector <vector<int>> adj(n);
	
	for ( int i = 1; i < n; i++ ){
		int u, v; cin >> u >> v;
		
		--u, --v;
		
		adj[u].push_back(v);
		adj[v].push_back(u);
	}
	
	vector <int> a(n);
	
	for ( auto &u: a ) cin >> u;
	
	for ( int i = 0; i < n; i++ ){
		for ( int j = 0; j < 2; j++ ){
			dp[i][j][0] = dp[i][j][1] = n + 1;
		}
	}
	
	auto dfs = [&](auto dfs, int u, int p) -> void{
		vector <int> x(2, n + 1), y(2, n + 1);
		
		x[0] = y[0] = 0;
		
		for ( auto &v: adj[u] ){
			if ( v != p ){
				dfs(dfs, v, u);
				
				vector <int> xx(2), yy(2);
				
				for ( auto k: {0, 1} ){
					xx[k] = min(dp[v][0][k] + x[0], dp[v][0][k ^ 1] + x[1]);
					yy[k] = min(dp[v][1][k] + y[0], dp[v][1][k ^ 1] + y[1]);
				}
				
				swap(xx, x), swap(yy, y);
			}
		}
		
		for ( auto k: {0, 1} ){
			chmin(dp[u][a[u] ^ k][0], x[k]);
			chmin(dp[u][a[u] ^ k ^ 1][1], y[k] + 1);
		}
	};
	
	dfs(dfs, 0, -1);
	
	int ans = min(dp[0][0][1], dp[0][0][0]);
	
	if ( ans == n + 1 ) return cout << "impossible\n", 0;
	
	cout << ans << '\n';
}

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