Submission #820034

#	Time	Username	Problem	Language	Result	Execution time	Memory
820034		MohamedAhmed04	The Xana coup (BOI21_xanadu)	C++14	100 / 100	61 ms	30192 KiB

xanadu

#include <bits/stdc++.h>

using namespace std ;

const int MAX = 1e5 + 10 ;

int arr[MAX] ;
int n ;

vector< vector<int> >adj(MAX) ;

int vis[MAX][2] ;
long long dp[MAX][2][2] ;

void dfs(int node , int par , bool toggle)
{
	if(vis[node][toggle])
		return ;
	vis[node][toggle] = 1 ;
	dp[node][toggle][0] = dp[node][toggle][1] = n+1 ;
	int cur = arr[node] ^ toggle ;
	long long sum0 = 0 , sum1 = 1 ;
	vector<long long>v[2] ;
	for(auto &child : adj[node])
	{
		if(child == par)
			continue ;
		dfs(child , node , 0) , dfs(child , node , 1) ;
		sum0 += dp[child][0][0] , sum1 += dp[child][1][0] ;
		v[0].push_back(dp[child][0][1] - dp[child][0][0]) ;
		v[1].push_back(dp[child][1][1] - dp[child][1][0]) ;
	}
	sort(v[0].begin() , v[0].end()) ;
	sort(v[1].begin() , v[1].end()) ;
	if((!cur))
		dp[node][toggle][0] = sum0 ;
	else
		dp[node][toggle][1] = sum1 ;
	for(int i = 0 ; i < v[0].size() ; ++i)
	{
		sum0 += v[0][i] ;
		if((i+1) % 2 == cur)
			dp[node][toggle][0] = min(dp[node][toggle][0] , sum0) ;
	}
	for(int i = 0 ; i < v[1].size() ; ++i)
	{
		sum1 += v[1][i] ;
		if((i+1) % 2 != cur)
			dp[node][toggle][1] = min(dp[node][toggle][1] , sum1) ;
	}
}

int main()
{
	ios_base::sync_with_stdio(0) ;
	cin.tie(0) ;
	cin>>n ;
	for(int i = 0 ; i < n-1 ; ++i)
	{
		int x , y ;
		cin>>x>>y ;
		adj[x].push_back(y) ;
		adj[y].push_back(x) ;
	}
	for(int i = 1 ; i <= n ; ++i)
		cin>>arr[i] ;
	dfs(1 , -1 , 0) ;
	long long ans = min(dp[1][0][0] , dp[1][0][1]) ;
	if(ans > n)
		cout<<"impossible\n" ;
	else
		cout<<ans<<"\n" ;
	return 0 ;
}		

Compilation message (stderr)

xanadu.cpp: In function 'void dfs(int, int, bool)':
xanadu.cpp:39:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   39 |  for(int i = 0 ; i < v[0].size() ; ++i)
      |                  ~~^~~~~~~~~~~~~
xanadu.cpp:45:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   45 |  for(int i = 0 ; i < v[1].size() ; ++i)
      |                  ~~^~~~~~~~~~~~~

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