Submission #760517

#	Time	Username	Problem	Language	Result	Execution time	Memory
760517		YENGOYAN	The Xana coup (BOI21_xanadu)	C++17	100 / 100	90 ms	32292 KiB

xanadu

#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
#include <cmath>
#include <map>
#include <string>
#include <ios>
#include <iomanip>
#include <deque>
#include <queue>
#include <list> 
#include <stack>

#define FASTIO ios_base::sync_with_stdio(0); cin.tie(NULL);
using ll = long long;
using namespace std;
vector<vector<ll>>gp;
vector<ll>v;
vector<vector<vector<ll>>>dp;
void dfs(ll u, ll p) {
  ll cnt = 1e18, lox = 1e18, ans = 0, ans1 = 0;
  for (ll& x : gp[u]) {
    if (x != p) {
      dfs(x, u);
      dp[u][0][0] += min(dp[x][0][0], dp[x][1][0]);
      dp[u][1][0] += min(dp[x][1][1], dp[x][0][1]);
      if (min(dp[x][0][0], dp[x][1][0]) == dp[x][1][0]) ans++;
      if (min(dp[x][0][1], dp[x][1][1]) == dp[x][1][1]) ans1++;
      cnt = min(cnt, abs(dp[x][0][0] - dp[x][1][0]));
      lox = min(lox, abs(dp[x][1][1] - dp[x][0][1]));
    }

  }
  if (gp[u].size() == 1 && u != 0) {
    if (v[u] == 0) {
      dp[u][0][0] = 0;
      dp[u][0][1] = 1e17;
      dp[u][1][0] = 1e17;
      dp[u][1][1] = 1;
    }
    else {
      dp[u][0][0] = 1e17;
      dp[u][0][1] = 0;
      dp[u][1][0] = 1;
      dp[u][1][1] = 1e17;
    }
  }
  else {

    dp[u][0][1] = dp[u][0][0];
    dp[u][1][1] = dp[u][1][0] + 1;
    dp[u][1][0]++;
    if ((v[u] == 1 && ans % 2 == 0) || (v[u] == 0 && ans % 2 == 1)) {
      dp[u][0][0] += cnt;
    }
    if ((v[u] == 1 && ans % 2 == 1) || (v[u] == 0 && ans % 2 == 0)) {
      dp[u][0][1] += cnt;
    }
    if ((v[u] == 1 && ans1 % 2 == 0) || (v[u] == 0 && ans1 % 2 == 1)) {
      dp[u][1][1] += lox;
    }
    if ((v[u] == 1 && ans1 % 2 == 1) || (v[u] == 0 && ans1 % 2 == 0)) {
      dp[u][1][0] += lox;
    }
  }
  long long inf = 1e18;
  dp[u][0][0] = min(dp[u][0][0], inf);
  dp[u][1][0] = min(dp[u][1][0], inf);
  dp[u][1][1] = min(dp[u][1][1], inf);
  dp[u][0][1] = min(dp[u][0][1], inf);
}
void solve() {
  ll n; cin >> n;
  v = vector<ll>(n);
  gp = vector<vector<ll>>(n);
  dp = vector<vector<vector<ll>>>(n, vector<vector<ll>>(2, vector<ll>(2)));
  for (ll i = 0; i < n - 1; i++) {
    ll u, v; cin >> u >> v;
    --u, --v;
    gp[u].push_back(v);
    gp[v].push_back(u);
  }
  for (ll i = 0; i < n; i++) {
    cin >> v[i];
  }

  dfs(0, -1);
  if (min({ dp[0][0][0],dp[0][1][0] }) > n) {
    cout << "impossible" << endl;
  }
  else  cout << min({ dp[0][0][0],dp[0][1][0] });
}
signed main() {
  FASTIO
    ll t = 1;
  // cin >> t;
  while (t--) {
    solve();
  }
}

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