Submission #867050

#	Time	Username	Problem	Language	Result	Execution time	Memory
867050		Ahmed_Solyman	The Xana coup (BOI21_xanadu)	C++14	100 / 100	50 ms	20560 KiB

xanadu

/*
In the name of Allah
made by: Ahmed_Solyman
*/
#include <bits/stdc++.h>
#include <ext/rope>
 
using namespace std;
using namespace __gnu_cxx;
#pragma GCC optimize("-Ofast")
#pragma GCC optimize("-O1")
//-------------------------------------------------------------//
typedef long long ll;
typedef unsigned long long ull;
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define PI acos(-1)
#define lb lower_bound
#define ub upper_bound
#define endl '\n'
#define all(v) v.begin(),v.end()
#define allr(v) v.rbegin(),v.rend()
#define sum_to(n) (n*(n+1))/2
#define pb push_back
#define pf push_front
#define fil(arr,x) memset(arr,x,sizeof(arr))
const ll mod=1e9+7;
int dx[8]={0,1,0,-1,1,1,-1,-1};
int dy[8]={1,0,-1,0,1,-1,-1,1};
//-------------------------------------------------------------//
ll lcm(ll a,ll b)
{
    return (max(a,b)/__gcd(a,b))*min(a,b);
}
void person_bool(bool x)
{
    cout<<(x?"YES":"NO")<<endl;
}
const int N=1e5+5;
vector<int>adj[N],color(N);
ll n,dp[N][2][2];
ll solve(int i,int c,int rev,int p){
	ll &ret=dp[i][c][rev];
	if(~ret)return ret;
	if(adj[i].size()==1 && i!=1){
		if(c==1){
			return ret=1e9;
		}
		else{
			return ret=rev;
		}
	}
	int opt=0;
	bool flag=0;
	ll sum=rev;
	for(auto ch:adj[i]){
		if(ch!=p){
			ll a=solve(ch,rev^color[ch],0,i);
			ll b=solve(ch,1^rev^color[ch],1,i);
			sum+=min(a,b);
			if(a==b){
				flag=1;
			}
			else if(a>b){
				++opt;
			}
		}
	}
	ret=1e9;
	for(auto ch:adj[i]){
		if(ch!=p){
			ll a=solve(ch,rev^color[ch],0,i);
			ll b=solve(ch,1^rev^color[ch],1,i);
			int u=opt-(a>b);
			if((c^(u&1))==0){
				ret=min(ret,sum-min(a,b)+a);
			}
			else{
				ret=min(ret,sum-min(a,b)+b);
			}
		}
	}
	return ret;
}
int main()
{
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
    #ifndef ONLINE_JUDGE
    //freopen("input.in", "r", stdin);
    //freopen("output.out", "w", stdout);
    #endif
    fast
    fil(dp,-1);
    int n;cin>>n;
    for(int i=0;i<n-1;i++){
    	int u,v;cin>>u>>v;
    	adj[u].push_back(v);
    	adj[v].push_back(u);
    }
    for(int i=1;i<=n;i++)cin>>color[i];
    ll ans=min(solve(1,color[1],0,0),solve(1,!color[1],1,0));
	if(ans>=1e9){
		cout<<"impossible"<<endl;
	}
    else{
    	cout<<ans<<endl;
    }
    return 0;
}

Compilation message (stderr)

xanadu.cpp: In function 'll solve(int, int, int, int)':
xanadu.cpp:53:7: warning: variable 'flag' set but not used [-Wunused-but-set-variable]
   53 |  bool flag=0;
      |       ^~~~

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