Submission #557965

#	Time	Username	Problem	Language	Result	Execution time	Memory
557965		AdamGS	The Xana coup (BOI21_xanadu)	C++17	100 / 100	75 ms	18424 KiB

xanadu

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define rep(a, b) for(int a = 0; a < (b); ++a)
#define st first
#define nd second
#define pb push_back
#define all(a) a.begin(), a.end()
const int LIM=1e5+7, INF=1e9+7;
vector<int>V[LIM];
int dp[LIM][2][2], T[LIM]; 
void DFS(int x, int o) {
	int dp2[2][2];
	dp2[0][0]=dp2[0][1]=0;
	dp2[1][0]=dp2[1][1]=INF;
	for(auto i : V[x]) if(i!=o) {
		DFS(i, x);
		int dp3[2][2];
		rep(a, 2) rep(b, 2) dp3[a][b]=INF;
		rep(a, 2) {
			dp3[0][a]=min(dp3[0][a], dp2[0][a]+dp[i][0][a]);
			dp3[0][a]=min(dp3[0][a], dp2[1][a]+dp[i][1][a]);
			dp3[1][a]=min(dp3[1][a], dp2[0][a]+dp[i][1][a]);
			dp3[1][a]=min(dp3[1][a], dp2[1][a]+dp[i][0][a]);
		}
		rep(a, 2) rep(b, 2) dp2[a][b]=dp3[a][b];
	}
	rep(i, 2) {
		dp[x][0][i]=min(dp2[i^T[x]][0], INF);
		dp[x][1][i]=min(dp2[i^T[x]^1][1]+1, INF);
	}
}
int main() {
	ios_base::sync_with_stdio(0); cin.tie(0);
	int n;
	cin >> n;
	rep(i, n-1) {
		int a, b;
		cin >> a >> b; --a; --b;
		V[a].pb(b);
		V[b].pb(a);
	}
	rep(i, n) cin >> T[i];
	DFS(0, 0);
	if(min(dp[0][0][0], dp[0][1][0])==INF) cout << "impossible\n";
	else cout << min(dp[0][0][0], dp[0][1][0]) << '\n';
}

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