Submission #898040

#	Time	Username	Problem	Language	Result	Execution time	Memory
898040		LCJLY	The Xana coup (BOI21_xanadu)	C++14	100 / 100	59 ms	23632 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
 
#define int long long
#define ld long double
#define show(x,y) //cout << y << " " << #x << endl;
#define show2(x,y,i,j) //cout << y << " " << #x << "  " << j << " " << #i << endl;
#define show3(x,y,i,j,p,q) //cout << y << " " << #x << "  " << j << " " << #i << "  " << q << " " << #p << endl; 
#define show4(x,y) for(auto it:x) cout << it << " "; cout << #y << endl;
typedef pair<int,int>pii;
typedef pair<pii,pii>pi2;

int n;
vector<int>adj[100005];
int arr[100005];
int dp[2][2][100005];

void dfs(int index, int par){
	array<int,2>counter;
	array<int,2>change;
	array<int,2>cnt;
	change={(int)1e14,(int)1e14};
	cnt={0,0};
	counter={0,0};
	for(auto it:adj[index]){
		if(it==par) continue;
		dfs(it,index);
		for(int x=0;x<2;x++){
			if(dp[0][x][it]<dp[1][x][it]){
				//no toggle is better
				counter[x]+=dp[0][x][it];
				change[x]=min(change[x],dp[1][x][it]-dp[0][x][it]);
			}
			else{
				//toggle is better
				counter[x]+=dp[1][x][it];
				change[x]=min(change[x],dp[0][x][it]-dp[1][x][it]);
				cnt[x]++;
			}
		}
	}
	
	//no toggle remain 0
	dp[0][0][index]=counter[0]+ ((cnt[0]^arr[index])%2? change[0]:0);
	dp[0][1][index]=counter[0]+((cnt[0]^arr[index])%2==0?change[0]:0);
	dp[1][0][index]=1+counter[1]+((cnt[1]^arr[index])%2==0?change[1]:0);
	dp[1][1][index]=1+counter[1]+((cnt[1]^arr[index])%2?change[1]:0);
}

void solve(){	
	cin >> n;
	
	int temp,temp2;
	for(int x=0;x<n-1;x++){
		cin >> temp >> temp2;
		adj[temp].push_back(temp2);
		adj[temp2].push_back(temp);
	}
	
	for(int x=1;x<=n;x++){
		cin >> arr[x];
	}
	
	dfs(1,-1);
	int hold=min(dp[1][0][1],dp[0][0][1]);
	if(hold>1e13){
		cout << "impossible\n";
	}
	else cout << hold;
	
	
}
 
int32_t main(){										
	ios::sync_with_stdio(0);	
	cin.tie(0);
	//freopen("redistricting.in", "r", stdin);
	//freopen("redistricting.out", "w", stdout);
	int t=1;
	//cin >> t;
	while(t--){
		solve();
	}	
}

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