Submission #673661

#	Time	Username	Problem	Language	Result	Execution time	Memory
673661		stanislavpolyn	The Xana coup (BOI21_xanadu)	C++17	100 / 100	89 ms	15016 KiB

xanadu

#include <bits/stdc++.h>
 
#define fr(i, a, b) for (int i = (a); i <= (b); ++i)
#define rf(i, a, b) for (int i = (a); i >= (b); --i)
#define fe(x, y) for (auto& x : y)
 
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define mt make_tuple
 
#define all(x) (x).begin(), (x).end()
#define pw(x) (1LL << (x))
#define sz(x) (int)(x).size()
 
using namespace std;
 
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
template <typename T>
using oset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define fbo find_by_order
#define ook order_of_key
 
template <typename T>
bool umn(T& a, T b) { return (a > b ? (a = b, 1) : 0); }
template <typename T>
bool umx(T& a, T b) { return (a < b ? (a = b, 1) : 0); }
 
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
template <typename T>
using ve = vector<T>;
 
const int N = 1e5 + 5;
 
int n;
ve<int> g[N];
bool a[N];
 
int dp[N][2][2];
 
void dfs(int v, int p) {
    bool leaf = 1;
    fe (to, g[v]) {
        if (to == p) continue;
        dfs(to, v);
        leaf = 0;
    }
 
    if (leaf) {
        dp[v][a[v]][0] = 0;
        dp[v][!a[v]][1] = 1;
        return;
    }
 
//    cout << dp[v][0][1] << "\n";
 
    // don't press
    ve<int> dp(2, 1e9), ndp(2, 1e9);
    dp[a[v]] = 0;
    fe (to, g[v]) {
        if (to == p) continue;
 
        fr (was, 0, 1) {
            umn(ndp[was ^ 1], dp[was] + ::dp[to][0][1]);
            umn(ndp[was], dp[was] + ::dp[to][0][0]);
        }
        fr (was, 0, 1) {
            dp[was] = ndp[was];
            ndp[was] = 1e9;
        }
    }
 
    umn(::dp[v][0][0], dp[0]);
    umn(::dp[v][1][0], dp[1]);
 
    fill(all(dp), 1e9);
    fill(all(ndp), 1e9);
    // press
    dp[!a[v]] = 1;
    fe (to, g[v]) {
        if (to == p) continue;
 
        fr (was, 0, 1) {
            umn(ndp[was ^ 1], dp[was] + ::dp[to][1][1]);
            umn(ndp[was], dp[was] + ::dp[to][1][0]);
        }
        fr (was, 0, 1) {
            dp[was] = ndp[was];
            ndp[was] = 1e9;
        }
    }
 
    umn(::dp[v][0][1], dp[0]);
    umn(::dp[v][1][1], dp[1]);
 
//    cout << v << " " << ::dp[v][0][0] << " " << ::dp[v][0][1] << " " << ::dp[v][1][0] << " " << ::dp[v][1][1] << "\n";
}
 
int main() {
#ifdef LOCAL
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#else
    ios::sync_with_stdio(0);
    cin.tie(0);
#endif
 
    cin >> n;
 
    fr (i, 1, n - 1) {
        int a, b;
        cin >> a >> b;
        g[a].pb(b);
        g[b].pb(a);
    }
 
    fr (i, 1, n) {
        cin >> a[i];
    }
 
    fr (i, 1, n) {
        fr (j, 0, 1) {
            fr (k, 0, 1) {
                dp[i][j][k] = 1e9;
            }
        }
    }
 
    dfs(1, -1);
 
    int best = 1e9;
    fr (i, 0, 1) {
        umn(best, dp[1][0][i]);
    }
 
    if (best == 1e9) {
        cout << "impossible\n";
        return 0;
    }
 
    cout << best << "\n";
 
    return 0;
}

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