Submission #655267

#	Time	Username	Problem	Language	Result	Execution time	Memory
655267		600Mihnea	The Xana coup (BOI21_xanadu)	C++17	100 / 100	99 ms	21788 KiB

xanadu

#include <bits/stdc++.h>

using namespace std;

const int N = (int)1e5 + 7;
const int INF = (int)1e9 + 7;
int n;
int v[N];
int cost[N][2][2];
int nw[2][2];
vector<int> g[N];

void minup(int& a, int b) {
  a = min(a, b);
}

void dfs(int a, int p = -1) {
  vector<int> kids;
  for (auto& b : g[a]) {
    if (b == p) {
      continue;
    }
    kids.push_back(b);
    dfs(b, a);
  }
  g[a] = kids;
  cost[a][0][0] = cost[a][0][1] = cost[a][1][0] = cost[a][1][1] = INF;
  cost[a][0][v[a]] = 0;
  cost[a][1][v[a] ^ 1] = 1;


  for (auto& b : g[a]) {
    nw[0][0] = nw[0][1] = nw[1][0] = nw[1][1] = INF;
    for (int apply = 0; apply <= 1; apply++) {
      for (int cur = 0; cur <= 1; cur++) {
        for (int apply_b = 0; apply_b <= 1; apply_b++) {
          minup(nw[apply][cur ^ apply_b], cost[a][apply][cur] + cost[b][apply_b][apply]);
        }
      }
    }
    for (int i = 0; i <= 1; i++) {
      for (int j = 0; j <= 1; j++) {
        cost[a][i][j] = nw[i][j];
      }
    }
  }
}

int main() {
  ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);

  ///freopen("___input___.txt","r",stdin);

  cin >> n;
  for (int i = 1; i < n; i++) {
    int a, b;
    cin >> a >> b;
    g[a].push_back(b);
    g[b].push_back(a);
  }
  for (int i = 1; i <= n; i++) {
    cin >> v[i];
  }
  dfs(1);
  int sol = INF;
  for (int x = 0; x <= 1; x++) {
    sol = min(sol, cost[1][x][0]);
  }
  if (sol == INF) {
    cout << "impossible\n";
    return 0;
  }
  cout << sol << "\n";
  return 0;
}

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