Submission #1093133

#	Time	Username	Problem	Language	Result	Execution time	Memory
1093133		juicy	The Xana coup (BOI21_xanadu)	C++17	100 / 100	46 ms	17176 KiB

xanadu

#include <bits/stdc++.h>

using namespace std;

#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif

const int N = 1e5 + 5, inf = 1e9;

int n;
int dp[N][2][2], f[2][2], a[N];
vector<int> g[N];

void dfs(int u, int p) {
  for (int i = 0; i < 2; ++i) {
    for (int j = 0; j < 2; ++j) {
      f[i][j] = dp[u][i][j] = inf;
    }
  }
  dp[u][a[u]][0] = 0;
  dp[u][a[u] ^ 1][1] = 1;
  for (int v : g[u]) {
    if (v ^ p) {
      dfs(v, u);
      for (int i = 0; i < 2; ++i) {
        for (int j = 0; j < 2; ++j) {
          f[j ^ i][0] = min(f[j ^ i][0], dp[u][j][0] + dp[v][0][i]);
          f[j ^ i][1] = min(f[j ^ i][1], dp[u][j][1] + dp[v][1][i]);
        }
      }
      for (int i = 0; i < 2; ++i) {
        for (int j = 0; j < 2; ++j) {
          dp[u][i][j] = f[i][j];
          f[i][j] = inf;
        }
      }
    }
  }
}

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

  cin >> n;
  for (int i = 1; i < n; ++i) {
    int u, v; cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
  }  
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
  }
  dfs(1, 1);
  int res = min(dp[1][0][0], dp[1][0][1]);
  if (res == inf) {
    cout << "impossible";
  } else {
    cout << res;
  }
  return 0;
}

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