Submission #731704

#	Time	Username	Problem	Language	Result	Execution time	Memory
731704		NintsiChkhaidze	The Xana coup (BOI21_xanadu)	C++17	100 / 100	125 ms	25096 KiB

xanadu

#include <bits/stdc++.h>
#define int long long
#define pb push_back
using namespace std;
 
const int N = 1e5 + 5,inf=1e9;
vector <int> v[N];
int c[N];
int dp[4][N][4];

void dfs(int x,int par){
	int valblack = 0,valblack0 = inf,parblack = 1;
	int valwhite = 0,valwhite0 = inf,parwhite = 0;

	for (int to: v[x]){
		if (to == par) continue;
		dfs(to,x);
		//black
		valblack += min(dp[0][to][1],dp[0][to][0]);
		if (min(dp[0][to][1],dp[0][to][0]) == dp[0][to][1]) parblack++;
		valblack0 = min(valblack0, abs(dp[0][to][1] - dp[0][to][0]));

		//white
		valwhite += min(dp[1][to][1],dp[1][to][0]);
		if (min(dp[1][to][1],dp[1][to][0]) == dp[1][to][1]) parwhite++;
		valwhite0 = min(valwhite0, abs(dp[1][to][1] - dp[1][to][0]));
	}

	parblack%=2;
	parwhite%=2;

	int color = 1 - c[x];
	int oppcolor = c[x];

	//x-ზე ოპერაციას ვაკეთებთ
	if (parblack){
		dp[oppcolor][x][1] = min(dp[oppcolor][x][1],valblack + 1);
		dp[color][x][1] = min(dp[color][x][1],valblack + valblack0 + 1);
	}else{
		dp[color][x][1] = min(dp[color][x][1],valblack + 1);
		dp[oppcolor][x][1] = min(dp[oppcolor][x][1],valblack + valblack0 + 1);
	}

	//x-ზე ოპერაციას არ ვაკეთებთ
	if (parwhite){
		dp[oppcolor][x][0] = min(dp[oppcolor][x][0],valwhite);
		dp[color][x][0] = min(dp[color][x][0],valwhite + valwhite0);
	}else{
		dp[color][x][0] = min(dp[color][x][0],valwhite);
		dp[oppcolor][x][0] = min(dp[oppcolor][x][0],valwhite + valwhite0);
	}
}
signed main (){
	ios_base::sync_with_stdio(0),cin.tie(NULL),cout.tie(NULL);
	int n;
	cin>>n;

	for (int i = 1; i < n; i++){
		int a,b;
		cin>>a>>b;
		v[a].pb(b);
		v[b].pb(a);
	}

	for (int i = 1; i <= n; i++)
		cin>>c[i]; //c[i] = 0 -> i-წვერო თეთრი ფერია

	for (int i = 1; i <= n; i++)
		for (int j = 0; j < 2; j++)
			for (int p = 0; p < 2; p++)
			dp[p][i][j] = inf;

	//j ნიშნავს i წვეროზე ოპერაციას ვაკეთებ თუ არა
	dfs(1,1);
	int ans = min(dp[1][1][1],dp[1][1][0]);
	if (ans == inf) cout<<"impossible";
	else cout<<ans;
}

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