제출 #1165821

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
1165821		fryingduc	The Xana coup (BOI21_xanadu)	C++20	100 / 100	32 ms	15692 KiB

xanadu

#include "bits/stdc++.h"

using namespace std;

#ifdef duc_debug
#include "bits/debug.h"
#else
#define debug(...)
#endif

const int maxn = 1e5 + 5;
int n, a[maxn];
int f[maxn][2][2];
vector<int> g[maxn];
int ff[2][2];

void dfs(int u, int prev) {
  f[u][a[u]][0] = 0;
  f[u][a[u] ^ 1][1] = 1;
  for (auto v : g[u]) {
    if (v == prev) continue;
    dfs(v, u);
    memset(ff, 0x3f, sizeof(ff));
    for (int i = 0; i < 2; ++i) {
      ff[i][0] = min(ff[i][0], f[u][i ^ 1][0] + f[v][0][1]);
      ff[i][0] = min(ff[i][0], f[u][i][0] + f[v][0][0]);
      ff[i][1] = min(ff[i][1], f[u][i][1] + f[v][1][0]);
      ff[i][1] = min(ff[i][1], f[u][i ^ 1][1] + f[v][1][1]);
    }
    for (int i = 0; i < 2; ++i) {
      for (int j = 0; j < 2; ++j) {
        f[u][i][j] = ff[i][j];
      }
    }
  }
//  for (int i = 0; i < 2; ++i) {
//    for (int j = 0; j < 2; ++j) {
//      debug(u, i, j, f[u][i][j]);
//    }
//  }
}

void solve() {
  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];
  }
  memset(f, 0x3f, sizeof(f));
  dfs(1, 0);
  int res = min(f[1][0][0], f[1][0][1]);
  if (res > 1e9) {
    cout << "impossible\n";
    return;
  }
  cout << res;
}

signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  solve();

  return 0;
}

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