Submission #882915

#	Time	Username	Problem	Language	Result	Execution time	Memory
882915		dosts	The Xana coup (BOI21_xanadu)	C++17	100 / 100	75 ms	25712 KiB

xanadu

#include <bits/stdc++.h>
using namespace std;
#define sp << " " << 
#define int long long
#define vi vector<int>
#define F(xxx,yyy) for (int xxx=1;xxx<=yyy;xxx++)
#define pii pair<int,int>
const int N = 1e5+1;

vi c(N);
vi edges[N];
int dp[N][2][2];

void dfs(int node,int par,int p,int pp) {
  if (dp[node][p][pp]!=1e9+5) return;
  int tog = c[node]^p^pp;
  dp[node][p][pp] = 1e9;
  int sm = 0;
  vi ones;
  for (auto it : edges[node]) {
    if (it != par) {
      dfs(it,node,0,p);
      dfs(it,node,1,p);
      sm+=dp[it][0][p];
      ones.push_back(dp[it][1][p]-dp[it][0][p]);
    }
  }
  if (!(tog)) dp[node][p][pp] = min(dp[node][p][pp],sm+p);
  if (ones.empty()) return;
  sort(ones.begin(),ones.end());
  for (int i=1;i<(int)ones.size();i++) ones[i]+=ones[i-1];
  int sz = ones.size();
  for (int i=2-tog;i<=sz;i+=2) {
    dp[node][p][pp] = min(dp[node][p][pp],sm+ones[i-1]+p);
  }
}

void solve() {
  int n;
  cin >> n;
  memset(dp,-1,sizeof dp);
  F(i,n-1) {
    int a,b;
    cin >> a >> b;
    edges[a].push_back(b);
    edges[b].push_back(a);
  }
  F(i,n) cin >> c[i];
  F(i,n) {
    for (int j=0;j<2;j++) {
      for (int k=0;k<2;k++) {
        dp[i][j][k] = 1e9+5;
      }
    }
  }
  dfs(1,1,1,0);
  dfs(1,1,0,0); 
  F(i,n) {
    for (int j=0;j<2;j++) {
      for (int k=0;k<2;k++) {
        //cout << i sp j sp k sp dp[i][j][k] << endl;
      }
    }
  }
  int x = min(dp[1][0][0],dp[1][1][0]);
  cout << (x>=1e9?"impossible":to_string(x)) << endl;
}
    
                  
                             
signed main() { 
  ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
  #ifdef Local
  freopen("in","r",stdin);
  freopen("out","w",stdout); 
  #endif
  int t = 1;
  //cin >> t;
	F(i,t) solve();
}

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