Submission #857548

#	Time	Username	Problem	Language	Result	Execution time	Memory
857548		iskhakkutbilim	The Xana coup (BOI21_xanadu)	C++17	100 / 100	86 ms	47968 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
 
#define int long long
#define ff first
#define ss second
#define all(a) a.begin(), a.end()
const int N = 2e5;
const int MOD = 1e9 + 7;
const int INF = 1e9 + 7;
int n;
int a[N + 1];
vector<int> g[N+1];
 
 
vector<vector<int>> dfs(int v, int par){
	if(g[v].size() == 1 and v != par){
		vector< vector<int> > res(2, vector<int>(2));
		res[a[v]][1] = res[!a[v]][0] = MOD;
		res[a[v]][0] = 0, res[!a[v]][1] = 1;
		return res;
	}
	vector< vector<int> > sub(2, vector<int>(2, 0));
        sub[0][1] = INF;
        sub[1][1] = INF; 
        for(int to : g[v]){
        	if(to == par) continue;
        	auto child = dfs(to, v);
        	vector< vector<int> > new_sub(2, vector<int>(2));
        	for(int i = 0;i < 2; i++){
        		new_sub[i][0] = min(sub[i][0] + child[i][0], sub[i][1] + child[i][1]);
        		new_sub[i][1] = min(sub[i][0] + child[i][1], sub[i][1] + child[i][0]);
			}
			sub = new_sub;
		}
        vector< vector<int> > to_ret(2, vector<int>(2));
        to_ret[a[v]][0] = sub[1][0];
        to_ret[a[v]][1] = sub[0][1] + 1;
        to_ret[!a[v]][0] = sub[1][1];
        to_ret[!a[v]][1] = sub[0][0] + 1;
        return to_ret;
}
 
main(){
   ios::sync_with_stdio(0);
   cin.tie(0); cout.tie(0);
	cin >> n;
	for(int i = 1;i < n; i++){
		int A, b; cin >> A >> b;
		g[A].push_back(b);
		g[b].push_back(A);
	}
	for(int i = 1;i <= n; i++){
		cin >> a[i];
		a[i] = !a[i];
	}
	auto ans = dfs(1, 1);
	int res = min(ans[1][1], ans[1][0]);
	if(res >= MOD) cout << "impossible";
	else cout << res;
	return 0;
}

Compilation message (stderr)

xanadu.cpp:44:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
   44 | main(){
      | ^~~~

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