Submission #1045488

#	Time	Username	Problem	Language	Result	Execution time	Memory
1045488		pcc	The Xana coup (BOI21_xanadu)	C++17	70 / 100	45 ms	27988 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;

int N;
const int mxn = 1e5+10;
int dp[mxn][2][2];
vector<int> tree[mxn];
int arr[mxn];

void dfs(int now,int par){
	for(int i = 0;i<2;i++)for(int j = 0;j<2;j++)dp[now][i][j] = mxn;
	vector<int> v0,v1;
	int s0 = 0,s1 = 0;
	for(auto nxt:tree[now]){
		if(nxt == par)continue;
		dfs(nxt,now);
		s0 += dp[nxt][0][0];
		s1 += dp[nxt][1][0];
		v0.push_back(dp[nxt][0][1]-dp[nxt][0][0]);
		v1.push_back(dp[nxt][1][1]-dp[nxt][1][0]);
	}
	sort(v0.begin(),v0.end());
	sort(v1.begin(),v1.end());
	int t = arr[now];

	int ts = s0;
	dp[now][t][0] = ts;
	for(int i = 1;i<v0.size();i+=2){
		ts += v0[i-1]+v0[i];
		dp[now][t][0] = min(dp[now][t][0],ts);
	}
	ts = s1;
	for(int i = 0;i<v1.size();i+=2){
		if(i)ts += v1[i-1]+v1[i];
		else ts += v1[i];
		dp[now][t][1] = min(dp[now][t][1],ts+1);
	}

	t ^= 1;

	ts = s0;
	for(int i = 0;i<v0.size();i+=2){
		if(i)ts += v0[i-1]+v0[i];
		else ts += v0[i];
		dp[now][t][0] = min(dp[now][t][0],ts);
	}
	ts = s1;
	dp[now][t][1] = ts+1;
	for(int i = 1;i<v1.size();i+=2){
		ts += v1[i]+v1[i-1];
		dp[now][t][1] = min(dp[now][t][1],ts+1);
	}
	return;
}

int 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;
		tree[a].push_back(b);
		tree[b].push_back(a);
	}
	for(int i = 1;i<=N;i++)cin>>arr[i];
	dfs(1,1);
	int 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)':
xanadu.cpp:28:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   28 |  for(int i = 1;i<v0.size();i+=2){
      |                ~^~~~~~~~~~
xanadu.cpp:33:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   33 |  for(int i = 0;i<v1.size();i+=2){
      |                ~^~~~~~~~~~
xanadu.cpp:42:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   42 |  for(int i = 0;i<v0.size();i+=2){
      |                ~^~~~~~~~~~
xanadu.cpp:49:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   49 |  for(int i = 1;i<v1.size();i+=2){
      |                ~^~~~~~~~~~

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 40 / 40
• Subtask 5: 0 / 30