Submission #894454

#	Time	Username	Problem	Language	Result	Execution time	Memory
894454		d4xn	The Xana coup (BOI21_xanadu)	C++17	100 / 100	83 ms	49784 KiB

xanadu

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

#define int long long

const int N = 1e5+5, inf = INT_MAX;

int n, dp[2][2][N]; // me he pulsado a mi mismo?, soy 0 o 1?, nodo
vector<int> adj[N];
bitset<N> bt;

void dfs(int x, int p) {
  vector<vector<int>> sum(2, vector<int>(2, 0));
  vector<int> mnSum(2, 0);
  vector<int> cnt(2, 0);
  vector<int> mnDif(2, inf);

  for (int& y : adj[x]) {
    if (y == p) continue;
    dfs(y, x);

    for (int i = 0; i < 2; i++) {
      for (int j = 0; j < 2; j++) {
        sum[i][j] += dp[i][j][y];
      }
    }

    for (int i = 0; i < 2; i++) {
      if (dp[0][i][y] < dp[1][i][y]) {
        mnSum[i] += dp[0][i][y];
        mnDif[i] = min(mnDif[i], dp[1][i][y] - dp[0][i][y]);
      }
      else {
        mnSum[i] += dp[1][i][y];
        cnt[i]++;
        mnDif[i] = min(mnDif[i], dp[0][i][y] - dp[1][i][y]);
      }
    }
  }

  if (!bt[x]) {
    dp[0][0][x] = mnSum[0] + (cnt[0] % 2 ? mnDif[0] : 0);
    dp[0][1][x] = mnSum[0] + (!(cnt[0] % 2) ? mnDif[0] : 0);
    dp[1][0][x] = 1 + mnSum[1] + (!(cnt[1] % 2) ? mnDif[1] : 0);
    dp[1][1][x] = 1 + mnSum[1] + (cnt[1] % 2 ? mnDif[1] : 0);
  }
  else {
    dp[0][0][x] = mnSum[0] + (!(cnt[0] % 2) ? mnDif[0] : 0);
    dp[0][1][x] = mnSum[0] + (cnt[0] % 2 ? mnDif[0] : 0);
    dp[1][0][x] = 1 + mnSum[1] + (cnt[1] % 2 ? mnDif[1] : 0);
    dp[1][1][x] = 1 + mnSum[1] + (!(cnt[1] % 2) ? mnDif[1] : 0);
  }
}

signed main() {
  ios::sync_with_stdio(false); cin.tie(nullptr);

  cin >> n;
  for (int i = 0; i < n-1; i++) {
    int x, y;
    cin >> x >> y;
    x--; y--;
    adj[x].push_back(y);
    adj[y].push_back(x);
  }
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    if (x) bt[i] = 1;
  }
  dfs(0, 0);

  int ans = min(dp[0][0][0], dp[1][0][0]);
  if (ans>= inf) cout << "impossible\n";
  else cout << ans << "\n";
}

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