Submission #906053

#	Time	Username	Problem	Language	Result	Execution time	Memory
906053		Mathias	The Xana coup (BOI21_xanadu)	C++14	100 / 100	66 ms	20564 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int MAXN = 1e5+7;
const long long INF = 1e9+7;
long long dp[MAXN][3][3];
bool t[MAXN], visited[MAXN];
vector<long long> g[MAXN];
long long n,a,b,c,d;
void DFS(int x,int f){
	visited[x]=1;
	if(t[x]){
		dp[x][1][0]=1;
		dp[x][0][1]=0;
	}
	else{
		dp[x][1][1]=1;
		dp[x][0][0]=0;
	}
	for(int i=0;i<g[x].size();i++){
		if(visited[g[x][i]]==1) continue;
		int s=g[x][i];
		DFS(s,x);
	}
	for(int i=0;i<g[x].size();i++){
		int s=g[x][i];
		if(s==f) continue;
		a=dp[x][0][0], b=dp[x][0][1], c=dp[x][1][0], d=dp[x][1][1];
        dp[x][0][0]=min(a+dp[s][0][0], b+dp[s][1][0]);
        dp[x][0][1]=min(b+dp[s][0][0], a+dp[s][1][0]);
        dp[x][1][0]=min(c+dp[s][0][1], d+dp[s][1][1]);
        dp[x][1][1]=min(d+dp[s][0][1], c+dp[s][1][1]);
	}
}
int main(){
	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	cin>>n;
	for(int i=1;i<n;i++){
		cin>>a>>b;
		g[a].push_back(b);
		g[b].push_back(a);
	}
	for(int i=1;i<=n;i++) cin>>t[i];
	for(int i=1;i<=n;i++){
		dp[i][0][0]=INF;
		dp[i][1][0]=INF;
		dp[i][0][1]=INF;
		dp[i][1][1]=INF;
	}
	DFS(1,0);
	if(dp[1][1][0]>n and dp[1][0][0]>n) cout<<"impossible\n";
	else cout<<min(dp[1][1][0], dp[1][0][0])<<'\n';
	return 0;
}

Compilation message (stderr)

xanadu.cpp: In function 'void DFS(int, int)':
xanadu.cpp:20:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   20 |  for(int i=0;i<g[x].size();i++){
      |              ~^~~~~~~~~~~~
xanadu.cpp:25:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   25 |  for(int i=0;i<g[x].size();i++){
      |              ~^~~~~~~~~~~~

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